…in the past when stocks averaged much lower than 10% returns, subsequent 15-year average returns worked their way back to the 10% level—and then typically moved higher. Similarly, when 15-year average returns were much higher than 10%, subsequent returns were lower. This pattern makes sense: When stocks have underperformed their long-term average for 15 years, they may well be cheap. And when you start with cheap prices, future returns should be higher. Conversely, when stocks have significantly outdistanced the 10% annual threshold over 15 years, stocks as a whole may be expensive, which can lead to lower future returns.