Blame passive — sticking money in an index fund — and momentum — buying the winners, selling the losers — investors for these market swings, David Kelly, J.P. Morgan Asset Management’s chief global strategist, said on a call Thursday.

The good news, he says, is that unless the swings are “validated by actual weakness in earnings or increases in interest rates…then they will fade,” and it’s probably time to buy.

The new year will bring the real test for stocks, says our call of the day, from Northman Trader’s Sven Henrich. “Earnings coming in January will likely not show the crisis markets appear to have priced in. If anything, in the short term, valuation excess has been removed by this correction,” he says in an email.

Indeed, a Wells Fargo report that says U.S. defined-benefit pension funds need to buy $64 billion in equities before year-end has been blamed in part for the wild ride by ZeroHedge and others. Those purchases are needed to balance big divergences between bond and stock performances.

Pension funds + you’re-no-Warren-Buffett passive funds and momentum players + juniors manning the desks = mayhem on Wall Street this week.