You've probably already forgotten about last week's wild sell-off

The global markets got rocked last Friday, with the Dow dropping 279 points, or 1.5%, and the S&P 500 ending the day lower by 1.1%.

Such big sell-offs often have investors wondering if it's the beginning of an extended downtrend in stocks, like a bear market.

But as the chart below from Oppenheimer's John Stoltzfus shows, we've had multiple market plunges this year. And yet we're still up by more than 1%.

Oppenheimer

According to long-term data reviewed by JP Morgan Funds' David Kelly, "Despite average intra-year drops of 14.2%, annual returns [have been] positive in 26 of 34 years."

This is not to say we'll avoid a bear market or even a crash.

All it means is that big sell-offs happen over time, especially during upward trending markets.