Stocks that run up over 100% usually end in a climax. You will see a gap up after the stock has already gone up. Usually, it is a climax of 20-50%. This is a time you should sell and not risk trying to get extra money. After the climax run, the stock will drop past its 50-day moving average and continue to drop. If you look up the charts, you can see this effect on stocks. Some of them are Yahoo, Broadcom, and many others. Looking back on history can help you understand the market a little more.