One of the key drivers of the subprime mortage crisis in the early 2000s was that after a while, the market was being propped up by investors who had no idea what they were getting themselves into. Lured in by promises of easy wealth, these investors kept investing in subprime mortgages—even as more sophisticated investors saw the writing on the wall and were scrambling to cash out. In an op-ed for the New York Times, Paul Krugman explains why he sees echoes of the subprime mortgage crisis in the current crypto boom.