For me, it would be drawing.
As a kid, I drew a little, but it was one of those things I always believed you needed a "natural talent" for. I met a guy at a show a few years back who was an amazing tattoo artist - he pulled up some of his work on his phone while we were talking about tattooing - and he told me he hadn't really ever had any skill growing up. When he was 18, he was a dropout with no clear life goals, no job and no place to go. A friend took him in and forced him to draw 6-8 hours a day and monitored his progress, ultimately taking him on as an apprentice at his shop after. I don't know how much of it was true, but that would be the ultimate dream.