Buffett is warning us that prosperity masks incompetence—a truth we forget during booms because success feels earned rather than circumstantial. When markets crashed in 2008, investors discovered that many fund managers had merely been riding a wave of cheap money and rising asset prices, not demonstrating genuine skill. The sharper insight here is about *timing's dishonesty*: we mistake a favorable environment for personal capability, which means we're likely overconfident about our own naked swimming. That's why the financially prudent don't celebrate too loudly during good years—they're already mentally preparing for the tide's inevitable return.