Quick answer: sequence-of-returns risk is the danger that poor market returns early in retirement — while you are withdrawing — permanently damage your portfolio, even if long-run average returns turn out fine. It is the single biggest reason identical savers get different outcomes.
This guide shows how the order of returns changes everything, and how Monte Carlo simulation and historical stress tests (1929, 1973, 2000, 2008) reveal your plan's true fragility.