about stock market performance is that the average certainly isn’t the norm. Market fluctuations of this magnitude aren’t nearly fully explained by the changing fortunes of companies, industries or economies. They’re largely attributable to the mood swings of investors. Lastly, the times when return is at the extremes aren’t randomly distributed over the years. Rather they’re clustered, due to the fact that investors’ psychological swings tend to persist for a while—to paraphrase Herb Stein, they tend to continue until they stop. Most of those 13 extreme up or down years were within a year or
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