The stock market may be the only exchange in which buyers rush in when prices are raised and stand back warily when prices are marked down. The few investors able to resist this herd psychology are called contrarians; they buy and sell when others won't. Anthony M. Gallea, a Senior Portfolio Management Director, and William Patalon III, a newspaper reporter, have written a guide for those who aim to join the contrarians' lonely ranks. The authors' first rule is never to buy a stock unless its price has dropped at least 50 percent from its 52-week high. Following this rule would have meant missing out on a lot of the fun during the 1990s, but it may serve investors well if the market's momentum stalls