In the 1930s, Benjamin Graham, the father of security analysis, likened investing in stocks to doing business with a manic-depressive. Little has changed over the decades. Indeed, stocks have been wackier than usual lately. In October 2007, the stock market began its worst fall since the Great Depression. There was widespread panic when Lehman Brothers failed in September 2008. By the time the market bottomed, Standard & Poor’s 500-stock index had plunged 55.3% from its peak.