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anvesh
Hello, there
Hi there, I'm Anvesh.
I'm the person who answers “wait, how does that work?” with a twenty-minute story, four made-up friends and a few buttons you can press. People have mostly stopped asking me quick questions. So I put the long answers here, where you can skip ahead and I can't tell.
Each block below is one of those answers, told as a story with you in it. Pick one, there.
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A story starring §A§
Bitcoin, block by block
§A§, let's invent Bitcoin together. No maths degree needed. We start with four friends and a notebook, hit a problem, fix it, hit the next one. Eight fixes later, you'll have built Bitcoin yourself.
Meet the cast
§A§That's you. Honest, curious, about to understand Bitcoin.
§A§, §K§, §M§ and §D§ are always buying each other coffee. Swapping cash every time is a pain, so they try something simpler.
They keep one shared notebook. Every time someone pays for someone else, they write a line, like “§K§ pays §M§ 30”. At the end of the month, they settle up.
Rule 1Everyone starts with 100 coins.
Rule 2Nobody can pay more than they have.
The friends' notebook
Your turn
Mission: get the notebook to say no. Try making §K§ pay 500.
Balances, worked out from the notebook
Big ideaNobody is holding any coins. The balances are just worked out from the notebook. If everyone trusts the notebook, the notebook is the money. That's Bitcoin in one sentence: a notebook of payments. A “bitcoin” is just a number in it.
Hang on. If anyone can write in the notebook… what stops me writing “§A§ pays §D§ 80”? Asking for a friend.
Uh oh
Press “Let §D§ write a fake line” above. The notebook accepts it. §A§ never agreed! Anyone can write a line in someone else's name.Let's stop §D§ →
Your toolkit so far
Shared notebook
Problem: anyone can write “§A§ pays §D§ 80”, even if §A§ never agreed.
Chapter 2 · Signatures
A signature only §A§ can make
On paper we'd ask §A§ to sign each line. But a normal signature looks the same every time, so §D§ could just copy it.
A digital signature is cleverer: it's a code that's different for every single line, and only §A§ can make it.
Private keyA secret pen
A long secret number. Only §A§ ever sees it. Never, ever shared.
Public keyA handwriting sample
Shown to everyone, so anyone can check if a signature really came from §A§'s pen.
To sign a line, §A§ mixes the exact words of the line with the secret pen. Out comes a code. Anyone can check that code against the public key. Two great things follow:
§D§ can't make the signature. He doesn't have the secret pen.
Change even one letter of a signed line, and the signature stops fitting.
Sign a line
Your turn
Mission: catch a cheat. Sign the line, then press one of the sneaky buttons.
Everyone's keys
Signature
Not signed yet
To keep things fast, this page does the checking in a simplified way. The real maths lets anyone check a signature using only the public key.
Why the “#4”? Without it, §K§ could copy one real signed line and paste it ten times to get paid ten times. Numbering every line stops that.
Big ideaOnly §A§ can approve payments from §A§. In Bitcoin, owning coins really means owning the secret key that can sign them away.
Uh oh
One notebook sits on the table. Who looks after it? If §K§ does, §K§ is the boss: he could rip out a page or refuse to write §M§'s payments. Whoever holds the notebook has all the power.Can we have no boss at all? →
Your toolkit so far
Shared notebookSignatures
Problem: one person holds the notebook, so that person is the boss.
Chapter 3 · Everyone keeps a copy
No boss: everyone gets their own notebook
New plan. Every friend keeps their own copy of the notebook. To pay someone, §A§ signs the line and shouts it to everyone. Each friend checks the signature and writes it in their own copy.
Nobody's in charge now. If §K§ loses his notebook, the others still have theirs. Bitcoin works exactly like this: thousands of computers worldwide, called nodes, each keep a full copy.
Four copies of the notebook
Your turn
Mission: press the buttons 1 to 4 and watch §D§ break the vote.
I've got 85 coins. I'll whisper “§D§ pays §A§ 80” to §A§ and §M§… and “§D§ pays §K§ 80” to §K§. Both have my real signature. Who's going to know?
That trick is called double spending: paying two people with the same coins. Now the copies disagree, and there's no boss to settle it.
The obvious fix is a vote: whichever version most people have wins. Among four friends, fine. But online, making a thousand fake accounts costs nothing. §D§ would win every vote.
Uh oh
We need a vote that can't be faked with made-up accounts. It has to cost something real, like time and electricity. To build that, we need one strange but simple tool. Meet the fingerprint machine →
Your toolkit so far
Shared notebookSignaturesEveryone has a copy
Problem: copies can disagree, and head-count votes can be faked with made-up accounts.
Chapter 4 · Fingerprints
A machine that fingerprints any text
Picture a machine. Feed in any text, short or long, and out comes a fingerprint: a jumble of 64 letters and numbers. Computer people call it a hash. Bitcoin's machine is called SHA-256.
Rule 1Same in, same out
The same text gives the same fingerprint on every computer, every time.
Rule 2Tiny change, total chaos
Change one letter and the fingerprint changes completely.
Rule 3No way to plan it
Like un-blending a smoothie. You can't work backwards. You can only try and see.
The fingerprint machine
Real SHA-256
Mission: change “20” to “21” and count the orange squares.
Its fingerprint
The same fingerprint as 256 tiny switches (dark = on)
Switches flipped by your last edit: 0 of 256
It's always about half the switches, roughly 128, with no pattern at all.
Big ideaRule 3 is the useful one. If we ask “find text whose fingerprint starts with 0000”, there's no shortcut. You can only keep guessing. Guessing takes time and electricity. That's the real cost we were looking for.
Next
Let's turn this machine into a guessing game, and only let people add a page to the notebook if they've won it. Build the puzzle →
Your toolkit so far
Shared notebookSignaturesEveryone has a copyFingerprints
Problem: we need a vote that costs real effort, so fake accounts are useless.
Chapter 5 · The puzzle
Want to add a page? Win the guessing game first
Payments get grouped onto pages, a few thousand at a time. In Bitcoin a page is called a block.
New rule: a page only counts if its fingerprint starts with a bunch of zeros. The payments won't give you zeros by luck, so every page has a spare box for a guess number (the nonce). Try 0, 1, 2, 3… fingerprinting each time, until one happens to give enough zeros.
It's like rolling dice until you get four sixes in a row: pure luck and stamina. The people doing the guessing are called miners.
Win the guessing game
Real SHA-256
Mission: become a miner. Solve a page that needs 4 zeros.
Fingerprint of the latest guess
Press Start guessing
0guess number
0guesses so far
65,536guesses needed, on average
Each extra zero makes it about 16 times harder. Try 2 zeros, then 5.
Here's the magic: finding the answer took thousands of tries, but checking it takes one. Anyone can fingerprint the page with that guess number and see the zeros instantly.
Big ideaA solved page is proof that real work was done, so it's called proof of work. Fake accounts are now useless to §D§: accounts don't solve puzzles, computers do. Bitcoin's real puzzle is so hard that the whole world's miners together crack one about every 10 minutes.
Uh oh
Each page proves work was done, but the pages are loose. What stops §D§ pulling out an old page and slipping in a different one he solved on the side? Glue the pages together →
Your toolkit so far
Shared notebookSignaturesEveryone has a copyFingerprintsPuzzle per page
Problem: pages are loose, so an old page could be swapped out.
Chapter 6 · The chain
Every page writes down the last page's fingerprint
Simple fix: before solving its puzzle, each new page copies down the fingerprint of the page before it. That links the pages in order, like a chain. Hence the name: blockchain.
Now watch what happens if someone edits an old page. Its fingerprint changes (one letter changes everything, remember?). Its zeros vanish. And the next page has the old fingerprint written on it, so that page breaks too. And the next. Like toppling dominoes.
Try to change history
Edit any page
Mission: break the chain, then fix it. In page 1 change “20” to “90”, then press Mine on each red page, in order.
Big ideaTo change one old payment, a cheat must redo that page and every page after it. In the real Bitcoin chain, old pages have hundreds of thousands of pages stacked on top. Changing them is practically impossible.
Fine. I won't edit your chain. I'll quietly build my own chain, in secret, where I never paid anyone. Mwahaha.
Uh oh
Now there could be two versions of history. Which one does everyone believe?Let the race begin →
Your toolkit so far
Shared notebookSignaturesEveryone has a copyFingerprintsPuzzle per pageChain
Problem: two competing chains can exist. Which one wins?
Chapter 7 · The race
Everyone follows the chain with the most work
Bitcoin settles it with one rule: always trust the chain with the most puzzle-work in it (usually the longest). This is the vote from chapter 3, made unfakeable. Every solved page is a vote, and you can only vote by doing real work.
Here's the life of a payment, start to finish:
§A§ signs a payment and shouts it to the network.
Miners put waiting payments onto a new page and start guessing.
The first to solve it shouts the finished page to everyone.
Every node checks it: real signatures, no overspending, enough zeros, the right link to the last page. All good? Add it.
Everyone starts on the next page. If two chains ever compete, everyone moves to the one with more work.
Now §D§'s plan. He pays §A§ for a phone, and §A§ hands it over. Meanwhile, §D§ secretly builds a chain where that payment never happened. If his secret chain gets longer, he reveals it, everyone switches (that's the rule!), and his payment vanishes.
§A§'s defence: wait a bit. Each new page stacked on top of the payment is a confirmation. The longer §A§ waits, the further behind §D§ starts.
§D§ versus the world
Simulation
Mission: protect §A§. Run a race, then try more confirmations.
13.2%chance §D§ ever catches up (from the formula in the original Bitcoin paper)
Honest
§D§
page with the paymentconfirmationsmore honest pages§D§'s secret pages
Big ideaAs long as honest miners have most of the guessing power, a cheat's chances collapse with every confirmation. That's why big payments usually wait about 6 confirmations, roughly an hour. And it's why people worry if any one group ever gets half the world's mining.
One last question
All of this needs lots of honest miners burning electricity. Why would anyone bother? And where did those first 100 coins come from? One answer solves both →
Your toolkit so far
Shared notebookSignaturesEveryone has a copyFingerprintsPuzzle per pageChainMost-work rule
Problem: why would anyone pay for electricity to solve puzzles? And where do coins come from?
Chapter 8 · The reward
Win the puzzle, get brand-new coins
Here's the deal. Whoever solves a page gets to write one special line at the top: “New coins go to me”. Nobody pays these coins. They're created fresh: the block reward. The winner also collects small fees people add to get their payments onto a page faster.
Why mine?It pays
You might win new coins and fees. That covers the electricity.
Where do coins come from?Puzzle prizes
In real Bitcoin nobody starts with 100. Every single bitcoin began life as a prize.
The prize shrinks over time. It started at 50 coins per page in 2009 and halves about every four years: 25, 12.5, 6.25, and 3.125 since April 2024. Keep halving forever and the total never passes 21 million.
Coins in the world, year by year
Drag the year
Mission: time-travel. Drag the year to 2040 or later.
3.125new coins per page
19.9Mcoins in existence
95%of the 21M limit
Dates up to 2024 are real; later ones assume a page every 10 minutes. The last tiny bit of bitcoin should appear around 2140. After that, miners earn fees only.
One last trick keeps things steady. If loads more miners join, pages get solved faster. So every 2,016 pages (about two weeks) every node checks the pace and adjusts the number of zeros needed. Too fast? Harder. Too slow? Easier. That keeps it at about one page every 10 minutes, whether there are ten miners or ten million.
Pages are chained by fingerprints, so history is locked.
7
Everyone follows the chain with the most work.
8
Winners earn new coins, capped at 21 million.
§A§'s Bitcoin passport
Collect all 8 stamps
0/8
Certificate
§A§
has reinvented Bitcoin from scratch: the notebook, the signatures, the copies, the fingerprints, the puzzle, the chain, the race and the reward.
Signed with a secret key by Anvesh · verified by everyone
Missed one? Each chapter's hands-on panel has a mission. Scroll up and try it.
Questions you might ask, §A§
So where are my bitcoins actually kept?
In the shared notebook, and nowhere else. Your “wallet” app doesn't hold coins. It holds your secret key, the thing that lets you sign them away. Lose the key and the coins sit in the notebook forever, untouchable. Let someone see it and they can spend them. That's why the recovery words a wallet gives you matter so much.
Does the notebook really store balances like “§A§: 115”?
Not quite. It's more like cash and change. Each payment uses up earlier payments you received and creates new ones, including change back to yourself, like paying with a big note. Your balance is the total of payments you've received and not yet spent. Each one can only be spent once, which makes double spending easy to catch.
If someone controlled half of all mining, could they steal my coins?
No. They could undo their own recent payments, and block other people's payments from getting onto pages. But they can't sign with your secret key, and every node rejects any page with a fake signature or coins from nowhere. Mining power decides the order of honest payments, not the rules.
What if two miners solve a page at the same moment?
For a few minutes, part of the network has one version and part has the other. Each miner keeps building on whichever arrived first. Soon one side gets the next page and becomes longer, and everyone switches to it. The payments on the losing page go back into the waiting pile. Another reason to wait for confirmations.
Why do payments sometimes cost more?
Each page has limited space. Miners pick the payments offering the best fee for the space they take. When lots of people want to pay at once, fees go up, a bit like surge pricing.
Is the “secret pen” real maths?
Yes. A secret key is just a huge random number. The public key is worked out from it using a kind of maths called elliptic curves, which is easy in one direction and practically impossible to reverse. Sharing the public key never reveals the secret one.
Two lines, four boxes
Thinking tools · a 6-minute read for §A§
Two lines, four boxes
Why the humble 2×2 is one of the most useful thinking tools ever invented. It fits on a napkin, too.
In one line
When a question feels messy, pick the two things that matter most, draw a cross, and name the four boxes. The mess becomes a map.
There's a moment in every consultant's life when they pick up a whiteboard pen, draw a big plus sign, and the room goes quiet. Half the room is impressed. The other half is wondering if they're being charged by the minute.
Here's the secret, §A§: that plus sign really is brilliant. And you don't need a whiteboard. A napkin works. So does the back of a takeaway menu.
The problem: one-line thinking
We usually judge things on a single line. Good or bad. More or less. Yes or no.
One line, two people, zero progress. They might both be right.
“Is she a good parent?” “Is this a good CV?” One line forces a fight. You say good, I say bad, and we're both a bit right, because we're secretly measuring different things.
The fix: add a second line
Take parenting. In the 1960s, psychologist Diana Baumrind stopped asking “good or bad?” and asked two separate questions instead. Later researchers, Eleanor Maccoby and John Martin, filled in the last box. The two questions:
How warm is the parent? Hugs, praise, “tell me about your day”.
How firm are the rules? Bedtimes, boundaries, “phones off at dinner”.
Firm rules
Authoritarian“Because I said so.”
Authoritative“Bedtime's at 8. Now come here, give me a hug.”
Uninvolved“Hmm? Sorry, I was on my phone.”
Permissive“Ice cream for dinner? Sure, sweetie.”
Warmth
Warmth across, rules up. Research tends to link the top-right box with the happiest, most confident kids.
Look what happened. On one line, “warm” sounds simply good. On the 2×2, you can see that warm with no rules is a different thing entirely: the parent who lets you have ice cream for dinner is very warm, and also a bit of a problem.
Side noteMost real parents visit all four boxes before 9am on a school day.
Why it works so well
1
It fits in your head.
Brains are good at juggling two things. Add a fifth and they start dropping plates.
2
It pulls apart things we lump together.
“Strict” and “loving” feel like opposites. They're not. They're two different dials.
3
The names stick.
“Permissive” is easier to remember than “high on dimension one, low on dimension two”.
4
It shows you which way is up.
Once you know your box, you know exactly which dial to turn.
Let's plot a CV
Say §A§ is applying for a job. Every line on the CV can be judged on two things: is it relevant to this role? And does it prove you made a difference?
Proven impact
Impressive, wrong job“Tripled sales at a bakery.” For a data role.
Shortlist it“Cut onboarding time by 40% at a company like yours.”
The bin“Hobbies: reading, travel, socialising.”
The job ad, copied“Responsible for stakeholder management.”
Relevant to the role
Every bullet point lives in one of these boxes. Only one box gets you an interview.
Now the 2×2 tells you how to fix things. To move a bullet up, add a result, ideally a number. To move it right, describe your real experience in the words the job ad uses.
Side noteRecruiters read a CV in seconds. Even fewer if the first line is “hard-working team player”.
Once you see them, they're everywhere
Some of the most famous ideas in business and psychology are just two lines and four good names.
Important
Plan itExercise. Calling Gran.
Do it nowPassport expires Friday.
Drop itDoomscrolling.
Hand it offMost meeting invites.
Urgent
Your to-do list. Often credited to President Eisenhower and made famous by Stephen Covey. The inbox lives bottom-right. A good life lives top-left.
Vibe
Instagram trapNeon sign. Swing seats. Sad pasta.
Date-night winnerBook three weeks ahead.
Why are we here?Airport, 6am.
Hidden gemPlastic chairs. Best curry of your life.
Food
Where to eat tonight. Settles family arguments in under a minute. Mostly.
Cares about you
Ruinous empathy“It was great!” (It wasn't.)
Radical candour“Cut slide 4. You've got this.”
Manipulative insinceritySmiles now, moans later.
Obnoxious aggression“That was terrible.”
Tells you straight
How people give feedback, from Kim Scott's book Radical Candor. Aim for top-right; most of us hide top-left.
Market growing
Question marksPromising. Hungry for cash.
StarsWinning in a hot market.
DogsSmall share, going nowhere.
Cash cowsBoring. Pays for everything.
Your market share
The BCG matrix, from Boston Consulting Group around 1970. No real dogs were harmed in the making of this strategy.
How to draw a good one
1
Pick two things that really matter to the question. Not two things that are easy to measure.
2
Make sure they're actually different. More on this in a second, because it's the classic mistake.
3
Every box should be possible. Ideally, you can name something real in each one.
4
Give the boxes names a friend would get. “Hidden gem” beats “Quadrant 4”.
The diagonal trap
If your two lines secretly measure the same thing, everything lands on one diagonal and two boxes stay empty. You've drawn a line wearing a square's costume.
Tall people have big feet. We knew that. Cheap-but-great, though? That's worth finding.
Where 2×2s fib (a little)
Every good tool has a warning label. Here's this one's.
Life is a slope, not four rooms. Someone at 49 and someone at 51 are neighbours, not enemies.
People move. The same parent is authoritative at breakfast and permissive by 6pm on a Friday.
Boxes describe behaviour, not people. “You're such a Dog” is not feedback.
Sometimes you need a third thing. That's when someone draws a cube, and everyone suddenly remembers another meeting.
Your turn, §A§
Next time you're stuck, choosing a job, a flat, a holiday, a sofa, ask one question: what are the two things that really matter here? Draw the cross. Name the boxes. See where things land.
Fair warning: you will become the person who draws 2×2s on napkins at dinner. I would know.
Say it like a story
Communication · a 6-minute read for §A§
Say it like a story
Situation, Complication, Resolution: the three-step trick that makes people actually read your email, and then say yes.
In one line
Start with what everyone already agrees on. Add the twist that makes it a problem. Then give your answer. Nod, worry, relief.
§A§, you've had this email. We all have.
From: Someone in OperationsSubject: Quick update (please read)
Hi all,
Following on from last week's sync, and further to the various points raised by stakeholders in the context of Q3 alignment, I wanted to circle back on a few items, some of which we touched on previously, and some of which may require further discussion going forward, in particular around timelines, which as you know have been…
Read by: nobody
By the time it gets to the point, you've made a cup of tea, drunk it, and forgotten what tea is. The point was in paragraph four. It was important.
Meet the fix
In the 1960s, Barbara Minto joined McKinsey, became one of its first female consultants, and spent years teaching very clever people to write things other people could actually follow. Her book, The Pyramid Principle, gave the world a simple shape for opening any message:
S
Situation
What we all already know and agree on. No surprises. Heads nod.
C
Complication
What changed, or what's gone wrong. Eyebrows go up. “Oh no. So what now?”
R
Resolution
Your answer. What we should do. Everyone exhales.
The reader's mood, plotted. You want them to feel the dip, so they're grateful for the climb.
You already know this shape
Every story you've ever loved works like this.
S
Once upon a time, there was a peaceful kingdom.
C
Then a dragon moved in and started eating the sheep.
R
A brave knight sorted it out. Sheep everywhere rejoiced.
So does every TV advert ever made: “Your kitchen is lovely (S). But look at that oven (C). Try MagicScrub (R).” The reason SCR feels natural is that humans have been telling stories this way for thousands of years. You're just borrowing the shape for an email.
Example: the dishwasher
§A§ wants the flat to get a dishwasher. Here's the version most of us send.
Flat 4B group chat
guys i think we should maybe look into dishwashers?? there was one on sale and also the sink is kind of gross and someone (not naming names) never washes up and i read they actually save water too and
who is “someone”
i wash up all the time??
Result: 47 messages, no dishwasher
Now the SCR version.
Flat 4B group chat
S We all cook most nights, which is honestly great.
C But washing up takes about 40 minutes a day, and it's now the number one cause of passive-aggressive notes.
R Let's split a £250 dishwasher. That's £62.50 each, and nobody writes “WHOSE PAN IS THIS” ever again.
deal
ordering it now
Result: dishwasher by Thursday
Same facts. Different order. The first one sounds like a complaint. The second sounds like a plan.
Example: the work email
From: §A§Subject: Move app launch to 14 March? Need your OK by Friday
S We're planning to launch the new app on 1 March.
C Testing found a payment bug that affects 1 in 20 users. Launching with it would mean refunds and some very angry reviews.
R I recommend moving the launch to 14 March. The fix is ready; we need two weeks to test it. Can you approve by Friday?
Approved in 4 minutes
Notice the subject line. It's the resolution. Busy people might only read the subject, so put your answer there.
Example: the family holiday
S
Every summer we go to the same beach, and it's lovely.
C
But last year it rained six days out of seven, and Dad read the same newspaper four times.
R
This year, let's try Portugal in June. Sunnier, similar price, and Dad can bring two newspapers.
Side noteResults may vary. Families are the toughest audience known to science.
Why it works so well
1
It starts with a yes.
People who are nodding are much easier to persuade than people who are already arguing.
2
The twist creates a question.
The complication makes the reader think “so what do we do?”. Your answer arrives exactly when they want it.
3
It's short.
Three parts fit in a text, a lift ride, or the first paragraph of an email.
4
It forces you to have a point.
If you can't write the R, you're not ready to hit send. Which saves everyone time, including you.
Side noteThis is why many meetings could have been an email, and many emails could have been nothing.
Pro move: for busy people, answer first
Minto's bigger idea was the pyramid: put your main answer at the top, with your reasons underneath. For a busy boss, flip SCR around and lead with the R: “I recommend moving the launch to 14 March. Here's why.” Then give the S and C as backup.
Minto's pyramid. Most people write it upside down: reasons first, answer last, reader gone.
Rule of thumb: use S → C → R when you need to bring people along. Use R first when they're busy and already know the background.
Four ways to get it wrong
The never-ending situation. “Since the dawn of time, humans have needed to wash dishes…” Get to the twist.
A complication that isn't one. “The weather's been nice” is not a problem. Unless you sell umbrellas.
No resolution. S and C with no R isn't a message. It's a moan. That's what group chats are for.
A situation they disagree with. If they're shaking their heads at line one, it's not a situation, it's an argument. Start somewhere you all agree.
Your turn, §A§
Next time you send something that matters, fill in the blanks:
S We all know that …
C But …
R So I suggest …
S: you've reached the end of the article. C: you'll now notice SCR everywhere, including in this sentence. R: go and use it.
Bitcoin, explained like you're 10
Money & maths · a hands-on read for §A§
Bitcoin, explained like you're 10
Plus a trip inside SHA-256, the magic blender that keeps Bitcoin honest. You'll get to drive it yourself.
Bitcoin is a notebook of who-owns-what that thousands of computers keep together. A blender called SHA-256 makes it impossible to cheat without doing a ridiculous amount of work.
Part 1Bitcoin in 8 small steps
Step 1
Money is a promise
Money works because everyone agrees it's worth something. If your whole class agreed that shiny bottle caps were valuable, bottle caps would be money. Weird, but true.
Step 2
Bitcoin is a list
There are no actual coins. Bitcoin is one giant notebook that says things like “§A§ sent Sam 2 bitcoins”. Your balance is worked out from the list.
Step 3
Everybody keeps a copy
Imagine every kid in the school has the exact same notebook. No teacher in charge. If one kid scribbles a lie, everyone else's copy shows it's wrong.
Step 4
A secret stamp
You get a magic stamp only you own (your private key). It makes a different mark for every message. Everyone can check the mark is yours using a picture of your stamp (your public key), but nobody can copy it.
Step 5
A magic blender
Throw in any text and it spits out a 64-character code, called a hash. Same ingredients, same code, every time. But change one tiny thing and the code is totally different. And you can't un-blend a smoothie. (Part 2 opens the lid.)
Step 6
A guessing game
To add a new page to the notebook, a computer must find a lucky number that makes the blender's code start with lots of zeros. There's no trick, only guessing, like rolling dice until you get ten sixes. These guessers are called miners.
Step 7
A paper chain
Every page writes down the code of the page before it. So the pages link up like a paper chain. Change an old page and its code changes, which breaks every loop after it.
Step 8
A prize for the winner
The miner who wins the guessing game gets brand-new bitcoins. That's the only way new ones are made, and there will never be more than 21 million.
Side noteThat's genuinely the whole idea. Everything else is details. Very clever, very nerdy details. Let's open the blender.
Part 2Inside the SHA-256 blender
Quick myth-buster: it's not encryption
Encryption
A locked box. Put a message in, lock it. Anyone with the key can open it and read the message again.
Hashing (SHA-256)
A blender. Put a message in, get a smoothie code out. There's no key. Nothing ever comes back out.
People often say “SHA encryption”, but SHA-256 is a hash function. It's a fingerprint maker, not a lock.
SHA-256 stands for Secure Hash Algorithm, 256 bits. It was designed by the US National Security Agency and published in 2001. Today it checks downloads, protects stored passwords, and powers Bitcoin. Here's how it works, in seven steps. Type anything into the X-ray machine and watch your words go through.
The SHA-256 X-ray machine
Real SHA-256
1
Letters become numbers
Computers can't read letters, so each one gets a number from a giant agreed list (called UTF-8). “A” is 65, “a” is 97, a space is 32.
2
Numbers become bits
Every number is written in binary: just 1s and 0s, eight per letter. Like a row of light switches.
3
Fill the lunchbox
SHA-256 eats in bites of exactly 512 bits. So your bits go in, then a single 1 as a “the end” marker, then 0s to fill the space, then the last 64 bits say how long your message was.
your messagethe “end” markerfiller zerosmessage length
4
Chop and stretch
The 512 bits are chopped into 16 “words” of 32 bits each. Then SHA-256 stretches them into 64 words by mixing earlier words together, so every word depends on lots of your message.
chopped straight from your messagestretched (mixed from earlier words)
5
Eight starting numbers
The blender starts with 8 fixed numbers, a to h. Where do they come from? The square roots of the first 8 prime numbers. Using such boring, public numbers proves the designers didn't hide a secret trick inside. Cryptographers call these “nothing up my sleeve” numbers.
6
64 rounds of mixing
Now the blending. In each round, everyone shuffles one seat along (a→b, b→c…), and two seats, a and e, get freshly mixed numbers made from the others, one of the 64 words, and a special constant. Drag the slider, or press Play.
Round 0 is the starting line: just the eight starting numbers.
7
Add up and read out
Finally, the mixed numbers are added back onto the starting numbers, and the eight results are stuck together. That's your 64-character fingerprint.
Your SHA-256 fingerprint
The five mixing moves
Inside each round, SHA-256 only uses five simple moves. Here they are on tiny 8-bit numbers (the real thing uses 32 bits).
Side noteFive moves, done 64 times, on numbers billions of times bigger. It's like a cake recipe that says “fold, flip, stir” and somehow produces a unique cake for every word in every language.
Why can't you un-blend it?
Two reasons, both simple.
1
Information gets thrown away.
If I tell you two numbers add up to 10, you can't tell me what they were. 3 and 7? 1 and 9? SHA-256 does tricks like that thousands of times, plus “rolling over” sums like a car's mileage counter.
2
There are too many possibilities to guess.
A SHA-256 fingerprint can be one of about 2256 values. That's a 78-digit number, roughly the number of atoms in the observable universe.
Mystery animal
Game
I've put a secret 5-letter animal into the blender. Here's its fingerprint. Can you work out which animal it was?
The secret fingerprint
Notice what just happened. Being “close” never helps: “tiger” and “tigers” look nothing alike once blended. The only way in is guessing. And if the list of possible answers is short (like 5-letter animals, or a weak password), a computer can guess them all in a blink. That's exactly why long passwords matter.
Part 3How Bitcoin uses the blender
A block's ID card
Every page of the Bitcoin notebook (a block) has a small summary at the top called the header. It's always exactly 80 bytes, which is tiny: about as much as this sentence. It holds six things:
verprevious block's fingerprintfingerprint of all paymentstimegoalguess
Version · which rules this block follows
Previous block's fingerprint · the paper-chain link
Fingerprint of all the payments · more on this below
Time · roughly when it was made
Goal · how small the fingerprint has to be (how many zeros)
Guess number · the “nonce”, the number miners keep changing
The 80-byte block header, drawn to scale. Miners blend it twice: SHA-256 of the SHA-256. Belt and braces.
Be a miner
Real SHA-256
Goal: find a guess number that makes the fingerprint start with 00. On average it takes 256 tries. Click one at a time to feel it, then let the computer go.
The block
Its fingerprint
0guess number
0tries so far
256tries needed, on average
Real Bitcoin asks for about 19 zeros at the start (strictly, a number below the goal). The world's miners together make more than a hundred billion billion guesses every second, and someone wins roughly every 10 minutes.
A fingerprint of fingerprints
A block can hold thousands of payments, but the header only has room for one fingerprint. The trick is a Merkle tree, named after Ralph Merkle, who invented it. Blend each payment. Then blend them in pairs. Then pairs of pairs, until one fingerprint is left at the top, the root. Change any payment, even by one coin, and the root changes.
Build a Merkle tree
Edit a payment
Root
Pair 1+2
Pair 3+4
Payment 1
Payment 2
Payment 3
Payment 4
Change “2” to “3” in payment 1 and watch the orange spread up to the root. Fingerprints are shortened to 8 characters to fit. Bitcoin blends each pair twice, too.
This lets a phone wallet check that one payment is in a block without downloading the whole block. It only needs the few fingerprints on the path to the root. Clever, right?
1
Bitcoin is a shared notebook, copied everywhere.
2
A secret stamp proves who sent each payment.
3
SHA-256 turns anything into a fixed 64-character fingerprint.
4
It's a blender, not a lock: no way back, only guessing.
5
Miners guess until the fingerprint starts with lots of zeros.
6
Each block holds the last block's fingerprint, so history can't quietly change.
Want the story version, §A§?
This was the how. For the why, follow four friends as they invent Bitcoin from scratch, one problem at a time, with missions and stamps to collect.
Games people play
People & psychology · a 7-minute read for §A§
Games people play
Why the same arguments keep happening, explained by a 1960s psychiatrist who noticed that grown-ups play games. Not fun ones.
In one line
A “game” is a conversation that looks normal but has a hidden purpose and a predictable bad ending. Spot the pattern and you can simply stop playing.
In 1964, a Canadian-born psychiatrist called Eric Berne published a slim book with a playful title: Games People Play. It was meant for therapists. It became a surprise bestseller, because everyone who read it said the same thing: “Oh no. I do this. My family does this. My whole office does this.”
Here's the idea, §A§, in plain English.
Step 1: You have three people inside you
Berne said that at any moment, each of us is talking from one of three “ego states”. Think of them as three voices in your head taking turns at the microphone.
P
Parent
Rules, judging and looking after. Sounds like your parents did. “You should…”, “Never…”, “Here, let me do that for you.”
A
Adult
Calm, curious, facts-first. Like a friendly computer. “What time does it start?” “What are our options?”
C
Child
Feelings, fun, sulks and creativity. The bit of you that's still 7. “Wheee!”, “It's not fair!”, “Do I have to?”
None of them is bad. The Child is where joy and creativity live; the Parent keeps you safe. Trouble starts when the wrong one grabs the microphone, or when two people's voices don't match.
Side noteYou can hear your Parent voice switch on the first time you say “Because I said so” to someone. Usually a small nephew. Usually with horror.
Step 2: Conversations are ping-pong
Berne called each back-and-forth a transaction. When the ball comes back from the voice it was aimed at, the conversation flows. When it comes back from a different one, it crosses, and things get spiky.
Smooth
A→A Have you seen my keys?
A→A On the kitchen table.
Adult to Adult, Adult back. Done. Keys found. Peace in our time.
Crossed
A→A Have you seen my keys?
P→C Why are you always losing things?!
A simple question got a telling-off. Now nobody's looking for the keys. Everyone's looking for an apology.
There's a third kind, and it's the important one: the ulterior transaction. The words say one thing; the real message, underneath, says another. That hidden layer is where games live.
Step 3: Everyone needs strokes
Berne said people are hungry for recognition, which he called strokes. A smile, a “thanks”, a “nice job” are positive strokes. A telling-off is a negative stroke. And here's the sad bit: a negative stroke beats no stroke at all. Ignored kids misbehave for exactly this reason. So do some adults in meetings.
Games are, mostly, a clumsy way of getting strokes: attention and drama, without having to ask for what we actually want.
So what is a game?
A game is a series of moves that looks like an ordinary conversation, but:
1
There's a hidden message under the polite one.
2
It follows a predictable script. You've had this exact conversation before.
3
There's a switch: a moment where someone flips roles.
4
It ends with a payoff: a bad feeling that somehow feels familiar. “See? Nobody can help me.”
The greatest hits
Berne described dozens of games and gave them memorable names. Here are six you've definitely seen. Possibly this week.
“Why don't you… Yes, but”The most famous game of all
I never have time to exercise.
Why don't you go before work?
Yes, but I'm not a morning person.
Why don't you go at lunch?
Yes, but my lunch is only 30 minutes.
Why don't you…
Hidden purpose: not to find a solution, but to prove nobody can help. Payoff: the helper gives up, exhausted; the player feels quietly justified. Way out: stop suggesting. Try: “Sounds tough. What do you think you'll do?”
“Kick me”Asking for trouble, then feeling hard done by
Someone keeps turning up late, “forgetting” things, or making the same mistake, until people snap at them. Then: “Why does everyone always pick on me?” Payoff: confirmation that the world is unfair. Way out: don't deliver the kick. Calmly name the pattern instead.
“If it weren't for you”Blaming someone for a limit you secretly like
“I'd have travelled the world if it weren't for you.” Often, the person quietly chose a partner who'd stop them doing the scary thing, and now gets to complain instead of trying. Way out: “What's stopping you now?”
“Ain't it awful”Bonding over how terrible everything is
The traffic, the weather, the youth of today, the council. Feels like connection, but nothing ever changes, and everyone leaves a bit grumpier. Way out: join in for a minute, then ask, “So what would make it better?”
“Now I've got you”Waiting for someone to slip up
A person sets a tiny trap, or waits for a small mistake, then pounces with huge outrage. A 2p overcharge becomes a crime against humanity. Payoff: righteous anger, which feels great. Berne's full title for this one is too rude for this website. Way out: own the slip simply. Don't defend; don't counter-attack.
“See what you made me do”Blame, delivered at the scene of the accident
You ask someone a question while they're carrying the tea. They spill it. “Look what you made me do!” Payoff: it's never their fault. Way out: don't accept the blame. Hand them a cloth. Adult to Adult.
Bonus: the drama triangle
A few years later, Stephen Karpman, a student of Berne's, drew a picture that explains why games feel like a soap opera. Most games have three roles, and people swap between them mid-conversation.
Karpman's drama triangle (1968). The rescuer who gets ignored becomes the persecutor. The victim snaps and becomes the persecutor too. Round and round it goes.
Side noteEvery family WhatsApp group runs on this triangle. Some run on it 24 hours a day.
How to stop playing
1
Notice the déjà vu.
If you think “we've had this exact argument before”, you're probably in a game. Naming it to yourself is half the battle.
2
Answer from your Adult.
Calm, curious, factual. It's very hard to keep a game going with someone who won't play their part.
3
Don't take the switch.
When the role flip comes (“Why are you attacking me?!”), don't jump into the next corner of the triangle.
4
Give real strokes.
People play games to get attention. Give it freely and honestly, and the games lose their point.
5
Ask for what you actually want.
“I'm stressed and I'd love some sympathy” is less dramatic than a game. It also works far better.
A fair warning
It's a lens, not lab science. Berne's ideas are hugely influential in coaching and therapy, but they come from a clinician's observations, not big controlled studies.
Don't use it as a weapon. “You're playing Kick Me again” is, ironically, a brilliant opening move for a new game.
Most people don't know they're playing. Games are habits, not evil plans. Be kind, including to yourself.
Your turn, §A§
This week, listen for a “Yes, but”. When you hear one, don't offer another suggestion. Just ask: “What do you think you'll do?” Then watch the game quietly fold.
If someone replies “Yes, but…”, congratulations. You've found the advanced level.
Peptides, minus the hype
Health & science · a 7-minute read for §A§
Peptides, minus the hype
A plain-English introduction to three peptides everyone's suddenly talking about: BPC-157, GHK-Cu and retatrutide. What they are, what's actually been proven, and what hasn't.
Not medical advice. This article explains the science and the rules; it doesn't tell anyone what to take or how. Two of these three have very little human testing, and none is a licensed medicine. Talk to a doctor before putting anything in your body.
In one line
Retatrutide has big, serious trials behind it but isn't approved yet. GHK-Cu has decent evidence as a skin cream, not as an injection. BPC-157 has lots of rat studies and almost no human ones.
First, what's a peptide?
Your body builds things from amino acids, little building blocks. String a few together like beads and you get a peptide. String hundreds together and fold them up and you get a protein.
Your body uses lots of peptides as messages: tiny notes that tell cells “you're full now”, “start repairing here”, “release some sugar”. Some of the most successful medicines of the last few years are lab-made copies of these messages. The weight-loss drugs Ozempic and Mounjaro are peptides.
Side noteSo “peptide” isn't a magic word. It's a size. Calling something “a peptide” tells you as much as calling something “a sentence”. Could be Shakespeare. Could be a parking ticket.
The evidence ladder
Before we meet the three, here's the single most useful tool for reading any health headline. Every treatment climbs the same ladder. The higher it gets, the more you can trust it.
5
Licensed medicine
Regulators checked it's safe and works
4
Big human trials
Thousands of people, with a placebo group
3
Small human studies
Dozens of people, often no comparison group
2
Animal studies
Mostly rats and mice
1
Lab dish
Cells in a petri dish
Lots of things that cure rats never work in people. Rats are, sadly, not tiny humans.
Meet the three
Peptide 1
BPC-157
“Body Protection Compound 157”. Nicknamed the “Wolverine peptide”.
Evidence
Mostly animal
What it is
A lab-made chain of 15 amino acids, based on a protein found in stomach juice.
What people hope
Faster healing of tendons, muscles and the gut. Popular with gym-goers and athletes.
What we actually know
Lots of promising rat studies. In humans, only a handful of tiny studies with about 30 people in total and no proper comparison groups. When FDA scientists reviewed it in 2026, they could find essentially one human study, an old conference summary.
Rules
Not approved as a medicine anywhere. Banned in sport by the World Anti-Doping Agency since 2022. In July 2026, a US FDA advisory panel voted 8 to 6 to recommend letting pharmacies make it, over objections from the FDA's own scientists. That's a recommendation, not a final decision.
Watch-outs
It seems to help grow new blood vessels, which is good for healing but could, in theory, also help hidden tumours. Products sold online as “research chemicals” may not contain what they claim.
Side noteWolverine healed instantly, never aged, and had metal claws. He was also fictional.
Peptide 2
GHK-Cu
The “copper peptide”. A favourite of skincare fans.
Evidence
Skin cream: small human studies
What it is
A tiny peptide, just 3 amino acids, holding a copper atom. Your body makes it naturally, and levels in blood drop as we age. Chemist Loren Pickart first found it in the early 1970s.
What people hope
Firmer skin, fewer wrinkles, thicker hair, better healing. Lately, people have started injecting it hoping for “anti-ageing” effects.
What we actually know
As a cream or serum, it's been sold and studied in people for decades. The studies are small and often paid for by cosmetics companies, but dermatologists compare its effects to well-known skincare ingredients like vitamin C. As an injection: no published human studies at all.
Rules
Fine as a cosmetic ingredient in creams. Not approved as a medicine. In the US, an FDA panel is due to look at the evidence for injecting it.
Watch-outs
Doctors have reported people who self-injected turning up with high copper levels, liver problems and infections. Most dermatologists say: stick to the cream.
Side noteFor once, the boring option (a cream) is also the sensible one. Boring is underrated.
Peptide 3
Retatrutide
Eli Lilly's experimental weight-loss drug. Nicknamed “triple G”.
Evidence
Big human trials
Ozempic / WegovyGLP-1
MounjaroGLP-1GIP
RetatrutideGLP-1GIPGlucagon
Think of each hormone as a lock that controls appetite or how much energy you burn. Each new drug opens one more lock.
What it is
A lab-made peptide that copies three of the body's “I'm full” and “burn energy” messages at once (GLP-1, GIP and glucagon). It's given as a weekly injection in trials.
What we actually know
This one has climbed high. In a 2023 trial, people on the top dose lost about 24% of their body weight in 48 weeks. In bigger phase 3 trials reported in July 2026, people lost around 20 to 23% over 80 weeks, compared with 3 to 4% on placebo.
Rules
Not approved anywhere yet. Lilly says it plans to ask the US regulator for approval in early 2027. Until then, it's only legally available in clinical trials.
Watch-outs
Stomach side effects are common: diarrhoea, nausea, vomiting. In one trial, about 1 in 7 people on the highest dose stopped because of side effects. “Retatrutide” sold online is not the trial drug, and nobody knows what's really in it.
Side noteThe real science here is genuinely exciting. Which is exactly why grey-market sellers want to borrow its name.
Side by side
BPC-157
GHK-Cu
Retatrutide
Size
15 amino acids
3 amino acids + copper
Dozens of amino acids, lab-tweaked
Hoped-for use
Healing injuries
Skin and hair
Weight loss
Highest rung
Animal studies (plus tiny human ones)
Small human studies (cream)
Big human trials
Licensed medicine?
No
No (cosmetic cream is fine)
Not yet
The grey market, explained
You'll find all three for sale online, often labelled “for research use only, not for human consumption”. That label is a legal loophole, not a safety check. Nobody has tested that the vial contains the right thing, at the right strength, without contamination. When people have tested online products, they've found some that don't.
Side noteIf a product's label says “not for human consumption” and the seller's Instagram shows humans consuming it, trust the label.
Five questions for any health headline
1
Was it tested in humans?
Or rats? Or cells in a dish? Look for the rung on the ladder.
2
How many people?
Twelve people is an anecdote with a spreadsheet. Thousands is evidence.
3
Was there a comparison group?
Without a placebo group, you can't tell the drug from time, hope or luck.
4
Who paid for it?
Industry-funded studies aren't automatically wrong, but they deserve a second look.
5
Where would the product come from?
A pharmacy with a prescription, or a website with a discount code?
The takeaway, §A§
“Peptide” isn't a magic word, it's a size. Some peptides are among the most important medicines of the decade; others are rat studies with great marketing. Ask which rung of the ladder it's on, and talk to a doctor before trying anything.
