In a more rational world, investors would buy and hold for the long term, because they understand that long-term returns require long-term investment. Markets would behave rationally and according to the Efficient Markets Theory: prices would reflect all available information, making it impossible to consistently purchase undervalued stocks and sell inflated ones. Assets destined to decline in price would do so inadvertently. The reality, of course, is quite different. Human judgement is fallible and based on a broad set of both rational and less-rational factors. Our financial survival instinct can make it difficult to stick with an investment strategy when...