I've been wondering what it is that attracts me (and many people like me) to purusits at the more creative end of the spectrum. I'm enjoying this 3D art thing immensely (to the point where six hours vanishes in a haze while I deal with a model) and (reluctance to spend days redoing material aside) Unholy Wars is proving to be an enjoyable challenge. Its not even that I'm learning anything any more - I already know how to speel (badly) and use MS Word, I've grasped the principles behind poser, applying models, textures, clothes, hair and so on and so forth. Now that I know all that I would normally be getting bored of it and moving on but that's not happening this time.
I think its because interests and activities that involve learning a skill are only challenging for a while but consistently producing interesting and attractive creative works will remain challenging forever.
Also, more often than not there is no physical activity involved.