By John Reese

Hoping for the best but preparing for the worst is a good rule-of-thumb, a maxim that can help us stay measured and mindful when it comes to dealing with life’s inevitable ups and downs. But it can be hard to think about potential downs when the ups have been around for a while—and the current, nearly nine-year-old bull market is a perfect example of that.

Related: Who Really is a Passive Investor?

Since March of 2009, the S&P 500, including dividends, is up over 350% as of this writing, and if the current run is sustained until August of this year, it will be the longest bull market in the history of the index. But nothing lasts forever, and the stock market is no exception–which highlights how crucial it is for investors to resist complacency and maintain a realistic perspective.

Here’s some perspective to consider: If you were to look at the day-to-day undulations in equity prices, you would see that stocks are positive just a little over half the time. In a 2016 article, Ben Carlson of Ritholtz Wealth Management wrote, “Stocks don’t make new highs every single day, so most of the time you’re going to be underwater from your portfolio’s high-water mark. This means there are plenty of chances to be in a state of regret when investing in stocks.” He points out that the last 90 years have seen bear markets almost one-quarter of the time. Half the time, he added, “you’re down 5% or worse. It’s difficult to appreciate this fact when looking at a long-term log scale stock chart that seems to only go up and to the right.”

The table below, courtesy of Yardeni Research, shows both corrections and bear markets (the texted in red) going back to 1928.