Good investors are wrong often. What separates them is that being wrong does not knock them out of the game. That is a sizing decision, made before you buy, and it matters more than almost any analysis you will do afterwards.
Risk is the chance of a permanent loss, and the size of that loss if it happens. Diversification spreads that risk across businesses that will not all fail for the same reason. Position sizing caps how much any single mistake can cost you.
What to look at
- Losses compound against you: a 50% fall needs a 100% gain to get back to even.
- Drawdown is the fall from a peak. Individual stocks commonly see 30–50% drawdowns even when the business is fine.
- Many investors cap a single new position at 2–5% of the portfolio, letting winners grow rather than starting large.
- Diversify across industries and risk drivers, not just tickers. Five chip stocks are closer to one bet than five.
- Decide your exit conditions before buying: what evidence would make the thesis wrong, and what you will do then.
The shape of it
Gain needed to recover = 1 ÷ (1 − loss) − 1
An example
With a $20,000 portfolio and a 4% cap, a new position is at most $800. If the company collapses by 60%, the portfolio loses $480, or 2.4%. Painful, but survivable and recoverable.
Where people go wrong
Averaging down without new evidence is how small positions become large losses. A lower price only helps if the thesis is still intact.
Nobody can control whether an investment works. You can control how much it costs you when it does not. Size every position as if you might be wrong, because sometimes you will be.