I was recently approached about setting up my own “special purpose acquisition company” (SPAC), which would allow me to secure financial commitments from investors on the expectation that I will eventually acquire some promising business that would prefer to avoid an initial public offering. In picturing myself in this new role, I mused that I could be doubly fashionable by also jumping into the burgeoning field of cryptocurrencies. There have been plenty of headlines about striking it big, quickly, so why not get in on the action?

Being a wizened participant in financial markets, I declined the invitation. The risin...