Stock Market Falls Because There’s Something Scarier Than Taxes,

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Wall Street has found something scarier than tapering, taxes, and

China Evergrande Group

combined. It’s called the 50-day moving average.

The predictions of impending doom from Wall Street’s talking heads continued this past week. The reasons for a pullback are many: The stock market has rallied for too long and has gone up too smoothly, the Federal Reserve is about to remove the bond buying that has helped prop markets up, taxes are ready to rise, economic data are slowing. None of it really left a mark.

But then the

S&P 500
dropped 0.6%, to 4432.99, over the week, while the

Dow Jones Industrial Average
fell 0.1%, to 34,584.88, and the

Nasdaq Composite
slumped 0.5%, to 15,043.97. For the S&P 500, it was the first close since June 18 below its 50-day moving average—a technical measure of the previous 50 days’ closes that often ends up acting as support or resistance and that currently sits at 4436.35. For traders, it was very frightening.

That the drop also occurred on options expiration day—when options bets expire and are rolled over, typically a volatile day—also makes the moment fraught. Since May, options expiration has been the time for the S&P 500 to make a quick test of its 50-day moving average before a bounce higher. And when I say quick, I mean quick, as it usually took the index a day, maybe two, to rebound.

“The 50-Day MA discussion has been pounded into our heads with every drawdown,” writes Frank Cappelleri, desk strategist at Instinet. “And while we may be sick of hearing about it, the dip buying around the line has been a real phenomenon.”

This time has a different feel to it. The S&P 500’s sojourn near the 50-day has been longer, notes Jonathan Krinsky, chief market technician at Bay Crest Partners. It’s been sitting near it for about six trading days now, without a big drop or big bounce. “The current set-up looks a bit more like a consolidation on the 50 DMA, as opposed to the prior quick ‘V-shaped’ dips,” Krinsky writes. “What we are saying is that the current way in which we got here feels a bit different than the last four to five times.”

Still, Krinsky acknowledges that one close below the 50-day isn’t enough to panic. That’s because the S&P 500 has now gone 218 days without two closes below the average, the…