During the first few months of this year—back when buying digital tokens named after dog memes was still seen, at least in some of the most forward-thinking circles, as a perfectly reasonable way to participate in finance’s bright new future—the cryptocurrency exchange Binance promoted a new, low-risk way to get in on the action. It urged its customers to invest in something called TerraUSD. The token was what’s known in the trade as a “stablecoin,” a type of cryptocurrency that functions a bit like a savings account and promises to always be worth $1. Binance told customers who used its service to buy, sell, and invest in various cryptocurrencies that this particular stablecoin offered something special: the promise of annual returns of almost 20%. TerraUSD, Binance suggested to customers, could be somehow both “safe” and “high yield.”