Consider: During the decade of the 1920s, big company stocks returned an average of 19.2%, according to Ibbotson — way above the long-term average. But the next decade was miserable, with returns on big company stocks dropping 0.1% over the 10 year period. In other words, if you invested $10,000, at the end of that decade, you would have a little less than $10,000 and probably feel demoralized. What happened then? In the 1940s, market returns were pretty manic — alternating between big losses and huge gains. The average return, however, ended at 9.2%. Still, because of the really rotten returns in the 1930s, investors could expect a “catch-up” decade and they got it. During the 1950s, average stock returns rose 19.4%.