One of history's most reliable stock-trading strategies is struggling

REUTERS/Neil Hall Buy low, sell high. It's a classic adage -- one that has helped stock investors reap consistent gains for the better part of seven decades. Until now. Having returned 5% on average each year from 1940 through 2007, the so-called value trade has lost 2% per year over the past decade, according to Goldman Sachs data. It's down 10% this year alone, badly lagging an S&P 500 that has climbed 8.7%. The decline of the value strategy has mirrored the rise of passive investing and quant...