Len, you're so kind to forgive me, if I needed it
Pete, the thing is, most of us can't help ourselves - writing wins every time. I think we just re-define 'comfortable living', and earn in order to write, not write in order to earn. And the tax advantages of being self employed help. One (not the only) of the reasons I decided to keep on with the PhD, even after I signed with Headline Review and Morrow, was because it should help me to develop the teaching/lecturing side of things. I really don't want the pressure to write more and faster than is good for my work, and I'm not relying on fiction to keep me in my old age, that's for sure.
Len's right about the film rights, but that's so, so, so rare. Mere options aren't huge amounts unless you're Michael Crichton, and the big majority of film options never turn into films.
Emma