• Warren Buffett in 2017 offered sage advice for when the stock market is falling: “Keep your head.” It comes from Rudyard Kipling’s 1895 poem “If.” Some investors have warned the U.S. economy is inching toward a correction, and Buffett had said “no one can tell you” when these major market moves may happen.

The U.S. stock selloff continues this week as investors question how much President Donald Trump’s proposed tariffs and other policies could impact the economy. Some investors have even questioned whether Trump’s moves could spiral the economy into a recession.

Even Trump admitted in an interview with Fox News on Sunday the economy was in a “period of transition” when asked if the U.S. was headed toward a recession.

“I hate to predict things like that, there is a period of transition,” Trump told Maria Bartiromo. “It takes a little time.”

Meanwhile, the S&P 500 Index, which tracks the performance of the 500 largest companies listed on the stock exchange, is down about 2% since the start of the week and almost 9% from its Feb. 19 peak. Even Goldman Sachs’ chief economist downgraded the entire U.S. economy this week.

But one of the most revered and storied investors in history has some sage advice for when markets are amiss.

“There is simply no telling how far stocks can fall in a short period,” Warren Buffett wrote in a 2017 letter to shareholders. But even when major stock drops happen, he suggested finding solace in Rudyard Kipling’s 1895 poem “If.”

“If you can keep your head when all about you are losing theirs… If you can wait and not be tired by waiting… If you can think—and not make thoughts your aim… If you can trust yourself when all men doubt you… Yours is the Earth and everything that’s in it.”

Buffett’s main point was to “keep your head,” or maintaining composure while markets move. In his letter, he was referring to major stock market declines, like during 2007–2009 when the S&P lost 50% of its value. Currently, the stock market isn’t close to such a severe decline, but the CBOE Volatility Index, which serves as Wall Street’s “fear gauge,” has spiked more than 80% since Trump took office.

How often do major stock selloffs happen?

While it can feel like a frenzy when it happens, stock market selloffs happen somewhat frequently. A market correction—defined as a decline of 10% or more from the most recent closing high—happens about every 1.8 years, according to stock market research company The Motley Fool. Since World War II, there have been 24 stock market corrections, data from Covenant Wealth Advisors shows.

The current market is dangerously close to a correction, with markets dropping about 9% from a peak in February. Deutsche Bank economist Jim Reid has warned the U.S. economy entered “correction territory” on Monday.

While the market ultimately avoided a correction earlier this week, “the latest declines still meant the S&P 500 hit a six-month low, which is the first time we’ve been able to say that since October 2022,” Reid wrote in a note viewed by Fortune’s Eleanor Pringle.

Adam Turnquist, chief technical strategist with investment firm LPL Investments, had actually warned in a Jan. 23 post a correction could be coming. At the time, markets were still rallying from a Trump bump.

“The last time the market entered an official correction was 309 trading days ago, spanning well beyond the average number of 173 trading days without a correction since 1928,” Turnquist wrote. Although the stock market was nearing record-high levels at the time and it seemed “premature to talk about a potential correction, bull markets are not linear, and corrections, though relatively improbable, are always possible.”

Buffett had issued a similar warning in his 2017 shareholder letter about the volatility of the stock market.

“No one can tell you when [corrections] will happen,” Buffett wrote in 2017. “The light can at any time go from green to red without pausing at yellow.”