A clean quantitative framing is this: a stop loss is a pre-commitment device, not a magic shield against losses. Mechanism: Stops work by forcing discipline, not by preventing loss. A stop set too tight gets triggered by noise. A stop set too loose defeats its purpose. Good stop design requires understanding the volatility of the position and the invalidation point of the thesis. Market translation: Setting a stop at 2% below entry on a stock with 3% daily volatility almost guarantees you get stopped out before the thesis can develop. Failure mode: The mistake is setting stops based on psychological comfort rather than on the asset's actual volatility and your thesis invalidation point. Review question: Before sizing up, identify whether the edge comes from cash flow, volatility, timing or balance-sheet structure. The point is not to memorize the label. The point is to know what variable is actually doing the work.