It depends on who is managing your money and what their investment strategy is. So many people, including “experienced money managers”, treat the stock market like it’s a blackjack table. Trying to capitalize on the rise and fall of stock prices which are often driven by investor enthusiasm; or lack thereof. They’re like dust in the wind.
“Buy low sell high” is a great slogan but a lousy investment strategy. Investments are a long game. When you, or whoever is managing your 401k, buys stocks they’re using your money to buy ownership in a business. Diversification, not having all your investments in one stock or even one industry matters. Long term viability of the businesses you invest in matters. Investing in good, sustainable business that are not overvalued (meaning the stock price exceeds the book value) matters.
You want someone managing your money who does their research, understands what they’re investing your money in, and knows that when stock prices go down, it’s the best time to pick up more good investments at a discount. Not to panic and sell everything. That’s almost always a losing strategy.
That said, Lots of 401k’s are invested in index funds which have a detailed investment strategy that the broker handling your 401k should be able to provide you with a copy of.