The arithmetic is taught in every intro book and forgotten by the people who most need it. Lose 10% of an account and you need 11.1% to break even. Lose 20%, you need 25%. Lose 50%, you need 100%. The recovery curve is convex, and it bends violently against the trader who lets it run.
That's the math. The math is not the problem.
What the asymmetry actually does#
A 50% drawdown is not "a 50% drawdown." It is a slow conversion of an operating account into a different account that happens to share the same login.
The risk profile that got you to the loss — position sizes, conviction levels, hold tolerance — was calibrated to a balance that no longer exists. Every dollar at -50% has to perform the work of two old dollars to undo what one new dollar undid. The tempting move is to upsize to compensate, which is how -50% drawdowns become -70% drawdowns. The disciplined move is to downsize, which is how the recovery takes three years instead of one.
Neither feels good. Both are mathematically correct in different regimes. The trader who hasn't worked out which one they're in before they need the answer will pick the wrong one.
The number you can actually defend#
Most operators cannot honestly defend a 30% drawdown. By 30% they are not running their strategy — they are running grief. The trades after the line stop being trades and start being attempts to be made whole, which is a different objective and a worse one.
The number you can defend is the one where you'd still recognise yourself trading the same way at the bottom of it. For most people that number is between 8% and 15%. Anything past it is a different person making decisions, and that person is usually wrong.
The discipline#
There is exactly one prophylactic that works. You decide the percent before you need to defend it, and you size every position so that the worst plausible cluster of losses lands shy of the line. Not at the line — shy of it. The line is for the unlikely day, not the typical month.
A drawdown isn't the trade that breaks you. It's the third trade after the trade that breaks you, when you're sizing up to recover. That's the one to plan for.