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.

U.S. stocks climbed near their all-time high after oil prices eased further on hopes that Israel's war with Iran will not damage the global flow of crude

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