In today's unstable market environment, it's too easy to let our pre-historic brains take over and follow the herd; that's what fight or flight is all about. When this happens, the investor typically has a tendency to sell when investments are beaten down, and buy when they've been too high for too long. For instance, you sell your stock at a loss, keep it in a money market account where it's not keeping up with inflation, then go back into the market when it's been high for a long time.