Volatility in the stock market is not new. But, even if one takes a broad perspective, the recent experience with GameStop is extraordinary. As we write, the story is far from over, with several U.S. stocks—like GameStop, AMC Entertainment and Express—still on something of a wild ride. The Securities and Exchange Commission seems poised to investigate. And, members of Congress are planning to hold hearings. We don’t have any particular insights into how or when this will end. That is, except to say that history teaches us that episodes like this typically end badly.

Since this is an unusual post, we begin with a very clear disclaimer: nothing in this blog should be construed either as investment advice or legal advice.

In our view, we can already draw three big lessons from the equity market events of the past week. The first is about how narratives and the limits to arbitrage can lead to unsustainable asset price booms. Second, short sellers are important for the efficiency of asset pricing and the allocation of capital. Moreover, with the ongoing rise of passive index investing, their potential role in keeping the U.S. equity market efficient will become more, not less, salient. Third, to keep the financial system safe and resilient, it is essential that clearing firms maintain sufficiently stringent margin and collateral requirements even if, on occasion, it limits a broker’s ability to implement trades for its clients….