In Ep. 22, Theoretically, the ability to make money on stocks involves two key decisions: buying at the right time and selling at the right time. In order to make a profit, you have to execute both of these decisions correctly. The return on any investment is first determined by the purchase price. One could argue that a profit or loss is made at the moment it's purchased; the buyer just doesn't know it until it's sold. However, while buying at the right price may ultimately determine the profit gained, selling at the right price guarantees the profit (if any). If you don't sell at the right time, the benefits of buying at the right time disappear. 

Many investors have trouble selling a stock, and sometimes the reason is rooted in the innate human tendency toward greed. However, there are several strategies that you can use to identify when it is (and when it isn't) a good time to sell. The most important thing about these strategies is that they attempt to take some of the human emotions out of the decision-making process.