Bubbles and crashes

Picture a small town with one bakery for sale. A buyer looks at the books, sees it earns about £100,000 a year, and pays roughly what that’s worth. The next buyer does the same. Nobody overpays, because a higher price means a worse deal — more money for the same loaf. This is the normal market you’ve met all course: the price goes up, buyers grow more reluctant.

Now watch what happens when that rule flips on its head.

Normally, a higher price repels buyers

Back in item 4 you learned that a price is just the last point where a buyer and a seller agreed. And item 8 gave you a yardstick for whether that price is sane: a business is worth what it can earn. Pay £100,000 for a bakery that earns £100,000 a year, and that’s a fair deal. Pay £400,000 for the same bakery, and you’re paying four years of profit for one year’s worth — a bad deal, and most buyers walk away.

That’s the gravity holding prices to earth. Each rise makes the next buyer think twice. The system self-corrects.

In a bubble, the rule reverses

A bubble is what happens when the rising price itself becomes the reason to buy.

Stop and feel how strange that is. People stop asking “what does this business earn?” and start asking “is the price going up?” If it’s going up, they buy — not because the bakery is worth more, but because they expect to sell to someone else for more tomorrow. Their buying pushes the price higher. The higher price pulls in more buyers, who push it higher still.

This is a feedback loop: an output (a higher price) feeds back as an input (more buying) that makes the output bigger. It no longer needs the business underneath. The price has detached from earnings and is running on the crowd’s belief that it’ll keep running.

The fuel is a feeling everyone has: the fear of missing out. Your neighbour doubled their money. The person at work won’t stop talking about it. Sitting out feels like the loss. So sensible people buy — not because they’re stupid, but because the loop is built to recruit them. That’s the part to hold onto: a bubble isn’t a crowd of fools. It’s ordinary people, each making a locally reasonable move, adding up to something detached from reality.

A worked example: the £100 bakery

Say a bakery is worth about £100 a share — that’s what its earnings justify (item 8’s yardstick). Watch the loop run.

• Round 1 — price £100. Fair. A few buyers notice it’s also been ticking up lately, and pile in. Price rises to £130.
• Round 2 — price £130. Now it’s “the thing that’s going up.” The story spreads; more buyers chase the rise. Price jumps to £180.
• Round 3 — price £180. Almost nobody is checking the earnings now. The reason to buy is the chart. Latecomers rush in. Price hits £250.

The business hasn’t changed. It still earns what justifies about £100. But the price says £250 — two and a half times the worth — because each rise recruited the next wave of buyers. Belief, not bread, is holding it up.

The snap

A loop that needs new buyers dies the moment they run out. And they always run out, because the pool of people willing to pay an ever-sillier price is finite.

The last buyers pay £250. There’s no one left behind them to pay £280. The price stalls. Stalling is enough — the only reason to hold was the expectation of more rise, and the rise just stopped. So someone sells. The price ticks down. Now the loop runs the other way: a falling price scares holders, who sell to get out, which pushes the price lower, which scares more holders. The fear of missing out becomes the fear of being left holding it.

£250 doesn’t drift gently back to £100. It overshoots, often below £100, because panic is as blind as mania — in a real crash, even sound businesses get sold, because frightened people dump whatever they can (this is item 9’s caveat: in a panic, correlations jump to one). The snap is faster than the climb. It always is.

The whole, and your seat in it

This pattern is old. Tulip bulbs in 1600s Holland, the stock craze before 1929, internet companies at the turn of the millennium — different objects, identical loop. Rising price recruits buyers, buyers raise the price, until the buyers run out and it reverses. The wrapper changes; the mechanism doesn’t.

It would be comforting to think you’d see it coming and stay out. But the loop works precisely because it pulls in clear-eyed people. Inside a bubble, the rise is real money your friends are really making, and the warnings sound like sour grapes. The two most expensive words in markets are “this time is different” — and they get said, with full sincerity, in every single bubble. You are not standing above the crowd watching it lose its head. You’re in the crowd, and the crowd is made of people exactly as reasonable as you. Seeing that won’t make you immune. But it might make you slower — to believe the rise is the reason, and to forget there’s a bakery under there worth about £100.