“Buy and hold” is the mantra of many investment gurus. Rather than try to time the market or pick win­ners and losers, they say, indi­vidual investors should put their money into a representative basket of stocks and forget about it. Good advice, says Ilia D. Dichev, an economist at the Uni­versity of Michi­gan’s Stephen M. Ross School of ­Business. What a pity it’s too simple for most people to follow.

The NASDAQ market, the main crash site of the Internet boom of the 1990s, would have produced handsome returns (9.6 percent annually) for a person who invested in 1973 and did nothing until 2002.