The debate over stablecoins has come a long way since Facebook announced the creation of Libra (now rebranded Diem) almost exactly two years ago.

An obscure corner of the digital sphere that was poorly understood then is now subject to increasingly intense scrutiny by central bankers, regulators and investors. The stakes, including for financial stability, are high. Market capitalization, or circulating supply, of the four leading U.S. dollar stablecoins alone exceeds $100 billion

But more intense scrutiny does not mean better understanding. Start with the belief that stablecoins are intrinsically stable because they are “fully collateralized.” The question, of course, is: collateralized by what?