A correction hasn't shaken the historic market rally yet, but Wall Street legend Byron Wien says it's "definitely" coming.
"A 10 percent correction could come along at any time, and particularly when the market has done as well as it's done. I mean basically it's gone straight up since Donald Trump was elected," Wien warned on Wednesday on CNBC's "Trading Nation."
If a correction of that magnitude were to hit today, the Dow would suffer a 2,400 point blow.
Wien, vice chairman of Blackstone's Private Wealth Solutions group, gives a 50 percent probability for a deep sell-off by year-end. He's been in the correction camp all year — and says he's concerned it hasn't happened yet.
"The market is overbought and investors are optimistic," said Wien. "An overbought market with optimistic investors is vulnerable, and the question is what triggers the vulnerability?"
It's not an easy answer, according to Wien. His hunch is a geopolitical development, such as a major conflict with North Korea, could trigger a correction by causing instability. But it's also possible the rally could just pause on its own.
"Maybe the market just spontaneously begins to fade," added Wien, who believes the markets are already borrowing performance from 2018.
Regardless of how it materializes, Wien doesn't see it as a sign that a bear market is around the corner. He believes stocks would bounce back quickly, and ultimately end 2018 higher than current levels.
"Fundamentals are very strong," Wien said.
The Dow, which is up 32 percent since Trump was elected, saw its second negative session in a row on Wednesday after falling about 40 points. It closed at 24,140.