Economist Mohamed El-Erian told CNBC on Monday it would take a big surprise to knock the U.S. stock market off its perch.
"You need a major shock or a major series of shocks to dislodge this market. This market is not dislodged easily," the Allianz chief economic advisor said on "Squawk Box."
Citing the potential "shocks" that he's worried about, El-Erian put North Korea "doing something not just brazen but really stupid and the U.S. reacting" at the top of his list.
He said he's also concerned about a possible monetary policy mistake, given the easy money that's been flowing since the 2008 financial crisis.
"I don't worry about the Fed " gradually continuing to hike interest rates or letting its $4.5 trillion balance sheet wind down, El-Erian said.
"People get complacent," El-Erian said, warning of "excessive risk-taking" due to investors being "conditioned" to believe that central banks will always have their backs.
"Buying every dip has made sense. And we know in the marketplace that nothing works better than something that consistently rewards you until it doesn't," he said.
The early promise of a "synchronized economic recovery" around the world "is not yet strong enough to warrant and validate existing asset prices," he said.
"We are at this level because of a tremendous injection of liquidity" by world central banks and companies in the form of stock buybacks, he said.
The wild card is whether these actions have bought enough time for the economic fundamentals the catch up to asset price levels, El-Erian said
"We're in the midst of a long and rewarding journey" with an unknown destination, he concluded.