The market’s plunge during late July and early August has left more than a few investors stunned. After all, the headlines certainly dramatize the drop and emphasize how unusual it was. And, indeed, it was a very sharp decline–the Dow fell nearly 17% in just 13 trading days! That said, one truism about the market is that the so-called unexpected actually occurs somewhat frequently. Said another way, unusually big moves–over a couple of weeks or an entire year–occur far more often than the media lead you to believe. For example, take the 10% return figure cited so often by...