Writing for Love or for Money?

I was recently emailing with a prospective client, and after I had told him about my editing process and what my terms are, he said, before I give the go-ahead, I'd like you to tell me frankly whether I'm going to make any money on this book. Well, I said, first of all, you should know that very few of all the published authors actually make much money on their books. So why does any one keep writing? Probably somewhere in his mind is the fantasy that his next novel will catapult him to stardom, as did The DaVinci Code with previously little-known Dan Brown. But I have a strong feeling that any real writer is writing because of love of the craft--because inside him there's a story he has to tell, an idea he has to develop, a period of history he has to research and write about, etc. So all of you writers out there: think about why you're writing. Is it for love or is it for money?