With U.S. markets slipping on Friday amid fears of a new Covid variant, you may be tempted to take some money off the table.

The Dow Jones Industrial Average is down 900 points for the day, or 2.5%. The S&P 500, meanwhile, has slid 1.8%. 

However, while selling today may reduce your stress at the moment, it’s likely to cost you in the long run, experts say.

“Pain is a sign you’re investing well,” said certified financial planner Allan Roth, founder of financial advisory firm Wealth Logic in Colorado Springs, Colorado.

If you can’t withstand the bad days, he said, you’ll also lose out on the good ones.

Over the last 20 or so years, the S&P 500 produced an average annual return of around 6%.

If you missed the best 20 days in the market over that time span because you became convinced you should sell, and then reinvested later, your return would shrivel to just 0.1%, according to an analysis by Charles Schwab.

“For longer-term investors, we suggest staying the course if they can,” said Rob Williams, CFP and vice president of financial planning at Charles Schwab.

Over the years, the market gives more than it takes.

Between 1900 and 2017, the average annual return on stocks was around 11%, according to calculations by Steve Hanke, a professor of applied economics at Johns Hopkins University in Baltimore.

After adjusting for inflation, that average annual return was still 8%. Along the way, the S&P 500 suffered at least 16 bear markets. (A bear market is typically defined as a decline of more than 20%.)

As a result, financial advisors caution against making any big changes to your investment strategy based any one period of declines.

We’re still waiting to learn more about what this new coronavirus variant will mean. But despite all the worrisome Covid headlines throughout the year, the S&P 500 Index was still up over 24% at the start of the month, according to Morningstar Direct.