I tend to take this 100-hour rule in short bursts. I can't often get myself to do something 2 hours a week consistently for a year (not to mention a decade!). So instead I tend to intensely apply myself to one thing for a short while, and then seldom do it after that. For example, I got into the habit of learning a new instrument every Summer for eight years. I tried everything from the guitar to the didgeridoo (I learned how to breathe circularly, too; it only took a week or so), and spent a Summer practicing whatever tickled my fancy. People really do find it impressive despite my insistence that I'm terrible at every instrument I play because I don't stick with it.

Moreover, I've found these minor skills have given me broad applications beyond what I originally intended (leisure). I worked at a day camp and knowing the harmonica and ukulele made campfire stories/skits/songs immeasurably better (I also did a semester of intense practice in performance literature, which helped as well). My forays into design have made me the resident web/design expert in my mathematics department, resulting in some extra cash. Learning to paint has made decorating my apartment way more fun and elevates my perceived sophistication (which I think is hilarious). The list goes on and I don't intend to stop growing it.