DAVOS, Switzerland—Bankers and executives at the World Economic Forum are celebrating a growing economy and rising markets. They see a continuing string of deals flowing their way, cost-saving new technology and a boost from U.S. tax cuts.

But underlying worries persist despite an upbeat economy in practically all corners of the world, said delegates on the sidelines of the event. Among them: The market’s ascent has been eerily, steadily calm.

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