Joseph Davis, the head of investment strategy at Vanguard, one of the largest asset-management companies in the world and the progenitor of passive investing, said he sees a "50% chance" of a correction - that is, a drop of 10% or more from the highs - next year.

While some joked about Davis's "coin flipper" odds...

...he explained that during more typical years, the odds of such a pullback are only 30%, and that stocks have a greater than usual chance of a double-digit pullback next year. We haven't seen a correction since, well, late last year, when stocks came a hair's breadth away from entering a bear market during the closing days of the year, culminating with one of the worst Christmas Eve sessions on record.