From Motley Fool:
Everybody loves a cheap stock. Everybody loves a popular stock — one with great name recognition.
Problem is, popular stocks are by definition stocks that attract a lot of attention from buyers, and that tends to drive the price up — making it hard to buy them on the cheap. Perversely, your best chance of getting a cheap price on a high-profile stock may not come until it’s made a high-profile stumble, causing its stock price to tumble.