Life can be full of surprises. Some are good, such as a bouquet of flowers for no reason from your spouse, or free lower-box seats to a baseball game from your neighbor. Other surprises are less so, like that cracked windshield from a stray pebble or an unexpected job loss.

Investing can result in its share of surprises, too--both positive and negative. Perhaps a pharmaceutical company's promising drug experiences poor study results, driving down the stock price. Or a company reports shockingly strong sales due to an unexpected event, leading to a rally in its shares.