A stock grabs attention when it doubles in a year. Yet, this creates a dilemma for both potential and current investors. The former feel like they've missed out and may be hesitant to buy at high levels. The latter might sell and take profits, but risk forsaking future gains. Stock prices typically rise when investors expect future earnings to increase, either because revenue grows, or profit margins improve, or both. Investors expecting future earnings to rise may then revalue a stock, attaching a higher m ...