"Two of the main reasons people sell stocks are because they go up and because they go down.When they go up, people who hold them become afraid that if they don't sell, they'll give back their profit, kick themselves, and be second-guessed by their bosses and clients. And when they go down, they worry that they'll fall further.
There may be absolutely no intellectual justification for that feeling. If you liked it a month ago at $80, should you sell it now just because it's at $60? The best way to get through a downdraft is to verify your thesis, tighten your seatbelt and hang on. If you sell just because there's a downdraft (or an updraft), you'll never get that twenty-year winner. When you look closely, you'll see that every twenty-year rise included a lot of ups and downs. To enjoy long-term success, you have to hold through them.