Fear of missing out is replaced by fear of staying in as crowded momentum stocks are purged

Traders work on the floor of the New York Stock Exchange (NYSE) on December 02, 2021 in New York City.

Spencer Platt | Getty Images

The market has been here before, and not long ago, the S&P 500 index undergoing a 5% setback after a nice rally to record highs, a shakeout that is moderating valuations and dousing investor overconfidence.