Goldman Sachs expects a 30% decline in the stock market, which would send the S&P 500 to about 4,300, or 18% lower from current levels.

If there's a core takeaway from eight decades' worth of stock market correction and bear market data for Wall Street's most widely followed stock index -- other than that history tends to rhyme on Wall Street -- it's that time in the market has consistently trumped trying to time its peaks and valleys.

You'll note the double-digit percentage declines in the S&P 500 and Nasdaq places both firmly in correction territory, with the Dow Jones not too far behind. These not-so-subtle moves lower are particularly surprising given how strong the stock market closed out President Donald Trump's first term in office.