That’s because the correlation between crude oil and stocks has not been stable over time. For several decades prior to 2000, for example, that correlation was negative, as you can see in the chart below. During those decades, higher oil prices in a given month led to below-average stock-market returns in the subsequent month.

Several headwinds threaten the U.S. stock market in the near term, but history says the S&P 500 is headed much higher in the long term.

Investors expected choppy markets on Monday. What they got was volatile, but in a way they didn't anticipate.