Michael Burry, whose credit-default-swap trade against the housing market brought him fame by way of Michael Lewis’s book The Big Short, returned to Twitter over the weekend after a months-long hiatus. The head of Scion Asset Management doubled down on his long-standing concerns about the rise of passive investing, citing a recently released working paper that found the stock market’s aggregate value tends to rise by about $5 for every $1 invested.

For years, investors on both Wall Street and Main Street have been throwing money into passive investment strategies like exchange-traded funds—hoping to capitalize on the belief that no one can consistently beat the market. There was a record $9.73 trillion of assets invested through ETFs, as well as exchange-traded products, globally at the end of August, marking a 21.8% jump from the end of 2020, according to research and consultancy firm ETFGI.

The flood of money into passive investing has come after years of stock pickers, by and large, failing to beat out the rest of the market. Earlier this year, S&P Dow Jones Indices found about 75% of large-cap funds in the U.S. underperformed the S&P 500 over the trailing five years leading up to the end of 2020.

Burry has long seen a bubble, though. In 2019, the hedge fund manager equated the swarm of money that has hit index funds to the rise of collateralized debt obligations in the lead-up to the financial crisis. “Like most bubbles, the longer it goes on, the worse the crash will be,” Burry said in an email exchange with Bloomberg at the time.

“The first step is to recognize that 5:1 is not a natural ratio,” Burry tweeted Sunday. “So what will continue this paradigm? What may reverse it? This is the knife’s edge, BECAUSE we are at 5:1. It may go to 100:1. Or become -5:1. But parabolas don’t resolve sideways.”

Passive investment vehicles are not the only part of today’s markets that are showing signs of a bubble in Burry’s eyes, though. In June, before deleting his tweets and quitting Twitter, Burry warned of “the mother of all crashes” that could come from investors throwing their money into cryptocurrencies and meme stocks. And in the second quarter, Burry also made a handful of bets against the ETFs of Cathie Wood’s ARK Invest, which are not passively managed.

On Saturday, in a since deleted tweet, Burry called for a boycott of Big Tech, while linking to the Wall Street Journal’s recent series, The Facebook Files. Scion held $327.3 million of call options on Facebook at midyear, according to its latest quarterly filing.

“Whether a little or a lot, please do,” Burry said. “For your health and the health of others.”

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