Great ideas mean nothing if one bad trade sinks the account. The simple sizing rules that separate consistent traders from blow-ups.
Ask any veteran what separates traders who last from those who blow up, and almost none will say stock-picking. They will say risk management — and at the heart of risk management is position sizing. It is the least glamorous skill in investing and by far the most important.
Survival first
The math of losses is brutal: a 50% drawdown requires a 100% gain just to break even. The primary job of position sizing is to make sure no single trade can do that kind of damage. If you risk a small, fixed percentage of your capital on any one idea, you can be wrong repeatedly and still be standing when the big winner arrives.
A simple framework
Decide in advance how much of your account you are willing to lose on a trade — often 1% to 2%. Your position size then falls out of the distance to your stop: the tighter the stop, the larger the position you can hold for the same risk. The idea is the same for everyone; the sizing is what keeps you alive.
The bottom line
You cannot control whether any single idea works. You can control how much it costs you when it does not. Master position sizing, and you give your edge the time it needs to play out. It is the skill that keeps you in the game.
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