At a guest lecture at a military academy when the price of a single Bitcoin neared US$60,000, I was asked, as finance professors often are, what I thought about cryptocurrencies. Rather than respond with my usual scepticism, I polled the students. More than half of attendees had traded cryptocurrencies, often financed by loans.

I was stunned. How could this population of young people come to spend time and energy in this way? And these students were hardly alone. The appetite for crypto has been most pronounced among Generation Z and millennials. Those groups became investors in the past 15 years at previously unseen rates and with exceedingly optimistic expectations.