I shared an office with a bunch of crypto enthusiasts in 2010 when I was running my first startup. They kept going on about Bitcoin and how I should get some because money would be obsolete in a few years. I thought they were silly (and I still do) but I could have a very different lifestyle now if I'd had some foresight.
It's not really a regret though. Just a missed opportunity. I'm a little more open-minded about tech now.