Bitcoin breaks my heart.
Not because I missed the great run-up (though I did) and not because I fear that the bitcoin bubble will end badly (it will, but that's not my problem). Rather, it is because I have been waiting for decades for someone to invent a purely digital currency, a currency for online purchases that wasn't linked to a credit card. It was the killer app that no one ever figured out.
Thus when bitcoin first emerged, I had hoped that it would be The One. In "Digital Gold," his book about bitcoin's origins, Nathaniel Popper quotes an email from Satoshi Nakamoto, the cryptocurrency's mysterious and possibly apocryphal inventor, "I've been working on a new electronic cash system that's fully peer-to-peer, with no trusted third party."