I draw when I can't sleep, which sort of means I'm an artist according to one of my profs from when I was still in school. To paraphrase him, J.C. Knaff, "You know [when you're an artist] when you'd rather draw than go to sleep." But I think all artist, of any kind (visual, written, musical, dramatic, etc.) have always said roughly the same thing, that what makes an artist is that drive to not quit and keep on going. I should get some sleep, I can badly philosophical when I don't have enough.