Multiple people beat me to the shoelace one, so here's one I don't see yet: running. At 48, I had hated running practically since I had first been able to do it, but I was in a situation where I decided to give it another try. I quickly figured out why I had hated it. I had been doing it wrong all my life. A little reading taught me about pacing and body lean and foot landings, and then ... well, it still kinda sucked TBH. But it sucked a lot less, in the way that anything hard will suck, and I've been able to stick with it year-round for almost nine years since. Still amazes me that I spent more than four decades doing something so basic so wrong. So much for being a smart guy, I guess.