Periods of sharp market volatility are an inevitable feature of investing. While for some it represents buying opportunities, for retirees, it brings into focus the unforgiving mathematics of drawdown, and the threat it represents to the sustainability of retirement incomes. This paper examines the mathematics in detail, and makes the case that limiting downside losses is not about inefficient defensiveness, or conservatism for its own sake, but rather should be a mathematical priority for retirement portfolios