Most investors come into the market with the belief that the best approach is a valid-oriented one. We should "buy low and sell high". So when stocks and the market are hitting new highs they are emotionally driven to sell . They want to redploy their money their money that are "bargains", which, for most people, simply mean "not their highs". The problems with this thinking is that for stocks to go higher and double and triple over time they have to trade at their highs. If you sell a stock when it hits a new high, how is it possible to hold any when it's doubling?