I had a co-worker take early retirement last year just as the COVID crash was bottoming out. Against my advice, he completely moved his 401k completely out of stocks because he felt the markets would keep crashing. Weeks later, as stocks recovered their value, he was kicking himself because he locked in his losses and lost hundreds of thousands of dollars of his portfolio. I told him he should move back in stocks but he didn't and so he missed out when the stock market shot to new highs. Now he is faced with the real danger of running out of money in retirement. He'll likely have to go back into the workforce.
It's a tough lesson to learn. As another poster here pointed out, even the experts cannot time the market. Us working folk shouldn't even try. Just hold your stocks for the long term and let dollar cost averaging and compound interest do its magic. The only tweaks I've ever done to my 401K over the past 40 years was slowly allocate more to safer funds as I age. But even now as I approach retirement age, I still have about a 60/40 split with 60% in stocks.
I was 100% out of stocks at beginning of March 2020. In May 2020 I was 100% back in stock index funds. It was NOT skill. It was pure luck.
It's astonishing how often this kind of scenario plays out -- even among people who should know better.
My theory is that a person's investment acumen is inversely proportional to the amount of time they spend watching TV.