This is the best reason of all to sell because it means you did something right and picked a winner. The key is to not let greed get in the way of smart portfolio management. If an investment is more than 10 percent to 15 percent of your portfolio, it’s time to think long and hard about trimming it down no matter how solid the company’s prospects may be. (These percentages are a rough guide—you might be comfortable with more money in a single stock, or you might want to be more diversified.)
