Yeah, that's true -- if the ego's not getting fed, by comments or cash, it's harder. I need feedback! (Or, sometimes, a push, if there's writing for pay involved. The sense that someone's there who is personally invested in seeing what I write.)

I'm not sure if I could write a total book without any feedback, unless I had a really Firm Idea. But writing it only for the feedback is disheartening, or writing something and not getting "enough" feedback is disheartening. (Where "enough" is a variable that depends on how invested I am in writing the thing in the first place. The less invested, the more feedback I need...)