It's been a rough couple of days on the stock market, but as any experienced investor will tell you, you have to expect these kinds of things. A correction - a 10 percent drop in value - is a regular occurrence in the markets.
Stock researcher Ed Yardeni has compiled a decade-by-decade record of how often these drops happen. This is the second correction since 2010, which is about par for the course. And barring a total meltdown like we had in 2008-09, the numbers usually don't get much worse than what we've already seen. Here's Yardeni's full chart: