Stop-loss is a bankroll management rule that establishes the maximum a player allows themselves to lose in a single session or day, typically 2-5 buy-ins in cash games or a fixed number of tournaments. The primary justification is psychological: continuing to play after large losses frequently results in tilt that leads to worse decisions, creating a downward spiral of further losses. In pure EV terms, if a player has positive EV, a stop-loss reduces volume and therefore total EV; but in practice, the deterioration of play quality post-loss justifies stop-loss for most players. Defining stop-loss before each session and rigidly adhering to it is a mark of professionalism and solid bankroll management.