Conversations and insights about the moment. [Video]

When the stock market has a bad day, as it did on Tuesday, experts come out of the woodwork to explain why “stocks fell.” A big move in the major stock indexes seems to require a big macroeconomic explanation, such as worries about economic growth.

In fact, by my calculation, more than a quarter of the decline in the S&P 500 stock index on Tuesday was caused by concerns about a single company, Nvidia, which supplies chips for artificial intelligence and other uses.

Nvidia lost $279 billion in market value on Tuesday, which was the biggest dollar loss for one company in one day in market history. Its sharp drop wasn’t mainly because of economic jitters. Traders seemed to be reacting to a report by Bloomberg that the Justice Department sent the company a subpoena as part of an investigation into whether it violated antitrust laws.

Looking slightly more broadly at Tuesday’s bad day, …