CNBC "Shark Tank" investor and chairman of O'Shares Investment Kevin O'Leary doesn't think the Trump rally will last. He told CNBC why during Thursday's "Halftime Report."

"Everything is fully valued, this is all about optimism," O'Leary said. "It's tonality, it's an animal spirit, there are no earnings changes whatsoever."

Additionally, he pointed to Facebook (FB) as a company starting to show "cracks" in the aftermath of the election, and the fact that it is "just an advertising platform," he said.

"I'm pointing out that all of this month, which was spectacular, was based on the premise that everything has changed overnight, and everything is going to be just wonderful in 2017," O'Leary contended.

Prospects of better interest rates, disappearing regulations, and oil staying above $50 per barrel, "that's not going to happen," O'Leary argued.

Considering his stance, O'Leary explained how he feels he can make 10% in Q1, shorting the regional banks. He called the run-up in these name "ridiculous."

"What will end the Trump rally? Reality," he added.