Grace K. Henry & Michael Sheehan

According to many studies, the mostcommon mistake the average investormakes is to buy high and sell low—chasinghot stocks and holding on to loserstoo long. Ask the average American,however, and you're likely to get a differentanswer—most Americans think theirmost common investment mistake isstarting too late. According to a survey byNational Research LLC, almost 50% ofall Americans say they postponed thestart of their investment program for toolong, while another sizable segment ruethe fact that they didn't invest enough.Holding on to losers was cited by onethird of those surveyed. Another third ofthose surveyed said they had too much oftheir portfolio wrapped up in a singleinvestment or stock.