Picking good companies is only half of investing. The other half — the half that decides whether you survive your mistakes — is how much you put into each one. Get sizing wrong and a single bad pick can undo years of good ones.
The maths of drawdowns
Losses and gains aren’t symmetric. Lose 50% and you don’t need 50% to get back — you need 100%. A 90% loss needs a tenfold gain to recover. This is why avoiding large, permanent losses matters more than chasing the last few percent of return: deep holes are punishingly hard to climb out of.
Diversification
Spreading money across many holdings (and, as you saw, across sectors) means no single failure sinks you. You give up the chance of one stock making your whole year — but you remove the chance of one stock ending it. For most investors that’s a trade worth making; a broad index takes diversification to its logical end.
Concentration — the trade-off
Some great investors do the opposite and concentrate in their few best ideas. It can pay spectacularly — but it demands deep conviction and an iron stomach, and it raises the odds of a serious drawdown. It’s a deliberate choice, not a default.
Sizing a position
Position sizing is simply deciding what fraction of your portfolio any one holding gets. A common discipline: size each position so that even a total loss on it wouldn’t be catastrophic. The goal isn’t to maximise this year’s return — it’s to stay in the game long enough for compounding to do its work.
Worked example
The drawdown maths, in numbers. Start with $10,000:
| Loss | Left | Gain needed to recover |
|---|---|---|
| −10% | $9,000 | +11% |
| −50% | $5,000 | +100% |
| −90% | $1,000 | +900% |
The deeper the hole, the punishingly larger the climb out. Now sizing: if your rule is that no single position may lose more than 2% of a $10,000 portfolio, the most any one holding can cost you is $200. Even a total wipeout of that position barely dents you — you live to compound another day. That’s the whole game: small enough bets that no single mistake is fatal.
The takeaway
Risk management is survival first: because a big loss needs an even bigger gain to undo, diversify to avoid single points of failure and size positions so no one mistake is fatal. Returns follow from not getting knocked out. (This is education, not investment advice.)