The fastest way to blow a prop-firm challenge is to over-risk a real edge. This experiment tested the same strategy at three risk levels and found only the smallest one survived out-of-sample.
Identical strategy, three position-sizing settings: 0.5%, 1.0%, and 1.5% risk per trade, evaluated on both a 6-week real-tick sample and a 6.4-month OHLC sample.
At 0.5% risk the strategy held a 5.2% six-month drawdown and a 1.16 profit factor — comfortably inside typical prop-firm limits. At 1.5% the drawdown ballooned to 12% and the edge broke down out-of-sample. Only 0.5% was robust across both samples.
Higher risk doesn't just scale returns — it scales variance faster than expectancy. A strategy with a genuine but modest edge can survive small position sizing and drown at large sizing, because a normal losing streak now breaches the drawdown cap before the edge can recover.
Size for the drawdown, not the dream. If your edge only looks good at 1.5% risk, you don't have an edge — you have leverage. Prop-firm-safe means the strategy passes at a risk level that respects the daily and total loss caps.