Drawdown

Drawdown measures how far equity has fallen from its highest point before recovering, usually expressed as a percentage. A peak of 10,000 falling to 8,000 is a twenty percent drawdown.

Recovery is mathematically harder than the loss: a fifty percent drawdown requires a hundred percent gain to return to break-even, and it must be earned on a smaller account. This asymmetry is the strongest argument for keeping per-trade risk small.