By some measures, equity markets are indeed “cheap” by historical standards. The cyclically adjusted price-earnings ratio (CAPE) of US stocks, pioneered by Nobel Prize-winning economist Robert Shiller, has fallen to its lowest level since June 2013. Equity market gyrations, meanwhile, have gone through the roof: Several of the biggest one-day gains and losses on record took place this month, according to Bianco Research. Some traders may be looking to speculate on price swings.

But not every company bounces back after a plunge. The stock of multinational conglomerate General Electric still hasn’t fully regained the ground it lost during the financial crisis in 2008; it took the S&P 500 Index about six years to attain its previous high.

Likewise, timing the market is nearly impossible, according to Rob Williams, vice president of financial planning at Charles Schwab. “People shouldn’t try to predict market highs and lows to decide when to start investing,” he wrote in an email to Quartz. He added:

“The trajectory over the long term has been upward, and if you aren’t invested you’re going to miss that growth. That said, we suggest that investors of any age who need a portion of their money in less than five years not invest that money in stocks. If you have larger purchases or expenses coming up in the next five years or so, market volatility demonstrates the need to reduce risk for that money and set it aside.”

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