Is the retirement industry's most-used measure of success also its most misleading? Probability of success reduces every outcome to a binary verdict, revealing nothing about the size of a shortfall or when it lands, and treating a modest miss late in retirement the same as a severe one early on. It also ignores the guaranteed income that establishes a spending floor and the flexibility retirees exercise as circumstances change. The better question isn't whether a plan passes or fails. It's how much of the goal actually gets funded. Through that lens, some retirees could spend 20% more in retirement without taking on additional risk.