"Many of the best days in the market come right after the worst days. According to the J.P. Morgan study, six of the 10 best days occurred within two weeks of the 10 worst days. One example was in 2015: The best day was Aug. 26, just two days after the worst day in the stock market that year."

You'd have to essentially ba perfect market timer to both sell at the top and re-invest prior to the rebound. It's not a prudent strategy.