There is a psychological bias against selling stocks: all buys are made in optimism, whereas not all sells conclude successful ventures. So selling is not a uniformly happy experience for stock investors. And virtually every sell, unless made at the historic high, at least sometimes looks like a wrong and irretrievably completed decision. Unhappy memories of such sales prompt avoidance behavior later. Sell the stocks on the way up, it is fine to leave some money on the table. In other words look at the technical and fundamental of the stock: if you wouldn't buy it at that point, it's the time to sell.