Many of us economists who believe in efficiency do so because we view markets as amazingly successful devices for reflecting new information rapidly and, for the most part, accurately.
Burton MalkielJ.P. Morgan once had a friend who was so worried about his stock holdings that he could not sleep at night. The friend asked, 'What should I do about my stocks?' Morgan replied, 'Sell down to your sleeping point' Every investor must decide the trade-off he or she is willing to make between eating well and sleeping well. High investment rewards can only be achieved at the cost of substantial risk-taking. So what is your sleeping point? Finding the answer to this question is one of the most important investment steps you must take.
Burton Malkiel