Over the last few weeks, investors reading the news headlines, tuning into CNBC or checking their account balances, have taken note of an uptick in volatility. It’s hard not to pay attention when markets turn choppy. Some begin to wonder if they should take action.

But market ups and downs—what investors call volatility—aren’t a sign that something is wrong. They’re a normal part of how investing works. We all want the long-term growth that comes from owning stocks. What we don't want are the uncomfortable stretches that come with it. Unfortunately, you can't separate the two. The superior long-term returns equities provide relative to other asset classes are available precisely because markets are uncertain and prices move around.

One of the most common questions investors ask is why a great company can report strong earnings and still see its stock price fall sharply. The answer often comes down to one word: expectations.

Over the long run, earnings growth is the primary driver of a company's stock price. However, in the short run, changes in investors' expectations about future growth can have an even greater impact. Understanding this relationship helps explain why some of the market's fastest growing companies can also be among its most volatile.