J.P. Morgan Private Bank is telling clients to buy the next sell-off, and the odds are high it'll happen this year.

Patrick Schaffer, a generally bullish global investment specialist at the firm, says a correction as deep as 14 percent would not surprise him.

"We don't expect the markets to go up in a straight line. When we do see volatility, we would be prepared to buy those pullbacks," Schaffer said Wednesday on CNBC's "Trading Nation."

The stock market hasn't seen a 10 percent or more sell-off in two years — an unusually long stretch even for a bull market.

If the Dow suffers a 14 percent blow now, it would take the index down nearly 3,500 points. would fall by 380 points, based on Wednesday's close.

What could spark it? Schaffer believes a geopolitical event or a more aggressive Federal Reserve could be catalysts.

But he doesn't see the pain sticking around because the tax overhaul and global backdrop are positive for stocks — particularly financials, industrials and parts of health care.

Schaffer, who manages more than $150 billion in assets, sees robust earnings as the rally's main driver now. According to his calculations, tax reform adds another 10 to 12 percent to S&P 500 earnings.

"The fundamental backdrop is as strong today as it's been at any point during this cycle," Schaffer said. "We think we can exit the year in the neighborhood of 3,000 in the S&P 500."