In July 1971, Michael Edesess, having received a Ph.D. in mathematics, started his first job, performing theoretical work on the stock market at a major brokerage firm. Within months he realized something was askew. The academic findings were clear and undeniable, but the firm—and the whole industry—paid no real attention to them. Theories and evidence both showed that professional investors could not beat market averages. A typical study in The Journal of Finance concluded: “The evidence on mutual fund performance discussed above indicates not only that … mutual funds were on average not able to predict security prices well enough to outperform a buy the-market-and-hold policy, but also that there is very little evidence that any individual fund was able to do significantly better than that which we expected from mere random chance.” Professional investors couldn’t even predict stock prices better than the nearest taxicab driver. Yet the entire business was based on the...