When I was in middle school, my group of friends would draw DBZ characters while in class. We would talk about yesterday's episode and procrastinate on school work, but it also developed into a contest of sorts. I don't think I realized it at the time, but deep down I wanted to draw the coolest stuff in the group.
This was my first taste of taking art seriously, beyond doing it just for recreation. It drove me to learn color, anatomy (even if it was incredibly exaggerated), posing, narrative, and so much more. Without that experience I don't think I would be where I am today.