Don't bet it all on one number

A man we’ll call Raj worked twenty years at a firm he believed in. Every year the company handed staff shares as a bonus, and every year Raj kept them — why sell stock in a company you trust from the inside? By his fifties, nearly all his savings, around £200,000, sat in that one company’s shares. Then the company missed a few quarters, lost a big contract, and went under. In a single bad year Raj lost his job and his life savings, because they were the same thing. He had made one bet, with everything, on one number. This lesson is about why that’s the most dangerous shape your money can take — and how spreading the same money across many bets quietly fixes it.

One bet means one bad event can end you

Put all your money on a single outcome, and your whole future rides on that one outcome going right. Not most outcomes. That one.

A single company can fail for reasons nobody saw coming — a fraud, a lawsuit, a new rival, a bad year. The odds of any one firm hitting disaster are low. But you only need one, and if it’s the one holding all your money, low odds are no comfort. The size of the loss is what gets you, not the chance of it.

This is the trap behind “I know this company.” Knowing it doesn’t lower the odds it fails. Plenty of people knew their employer well, right up to the day it collapsed. Familiarity feels like safety. It isn’t. It’s just one bet wearing the costume of a sure thing.

Spreading keeps the average, kills the range

Here’s the part that feels like magic but is just arithmetic. Spreading your money across many independent bets — bets whose fortunes don’t rise and fall together — leaves your average return untouched while it shrinks the range of what can happen.

Think about why. If you hold one company and it can either double or go bust, your outcome is wild: triumph or ruin. Now hold a hundred companies instead, the same total money split among them. They won’t all double, and they won’t all go bust. A few crash, a few soar, most land in between. The disasters of some are cancelled by the wins of others. You end up near the average of all of them — and the average was always there. What disappeared is the chance of the extremes. You no longer live or die on one roll of the dice.

Crucially, you didn’t give anything up. The expected return — the average outcome — is the same whether you bet it all on one or spread it across a hundred. Diversification doesn’t lower what you can expect to make. It lowers how badly wrong any single piece of bad luck can take you. That’s rare in money: usually less risk means less reward. Here, you cut the risk for free.

Walk the numbers

Say you have £20,000.

All on one company. If that company halves, you have £10,000 — a £10,000 hole. If it goes bust, you have nothing. Your entire future hangs on one firm’s luck.

Split across 100 companies, £200 each. Now suppose one of them goes bust completely. Your loss is £200 — a rounding error against £20,000. For it to wipe you out, dozens of unrelated companies would all have to fail at once, which is a different and far rarer kind of event. Meanwhile the average return across the hundred is exactly what you’d have expected from any one of them. Same expected outcome. A vastly narrower range. The ruin scenario is gone.

That’s the whole trick: identical average, the catastrophe edited out.

The employer trap stacks two risks into one

Now the sharpest version of the mistake — the one that caught Raj. Holding a lot of your employer’s stock isn’t just under-diversified. It’s actively stacking two risks that should be kept apart.

Your job is already a bet on that company. If it fails, your income stops. That’s one exposure you can’t easily avoid — you work there. So the last place you want your savings is in the same company. Put them there and a single corporate collapse takes your salary and your nest egg in the same blow. The two things you’d most want to fail at different times are now wired to fail at the same time.

Spread properly, a bad year at work is survivable — your savings sit safely in a hundred other places. Concentrated in your employer, a bad year at work becomes the worst year of your life. Same event, opposite outcome, decided entirely by whether you stacked your bets or spread them.

On the whole

Diversification is one of the rare free improvements in all of money. It doesn’t ask you to predict winners, time the market, or be clever. It asks you to not be destroyed by being wrong about any single thing — because you will be wrong about some things, and the only question is whether one of them can take everything.

The goal was never to be right about one bet. It’s to survive being wrong about any one of them. A single concentrated position — most of all in the company that already signs your paycheque — quietly ties your whole future to one roll of one die. Spreading the same money across many independent bets unties it: same average, far less to lose. You don’t escape uncertainty; nobody does. You just stop letting a single piece of it reach all the way to the bottom of what you have.