When you write, you get stressed out without a project. I got a very pleasant surprise when my ploy of sending my education title about archaeology to a publisher worked. It was accompanied by a note saying, "This has sold 31,000 copies so far, got any work for me?" As it happened, my former editor from Allen and Unwin, who is now series editor for a sort of junior version of the True Stories series, for which I wrote two books, did have some work for me and was pleased to hear from me. So I'm working on a juvenile book about spies. It's surprised me how quickly I've managed to get through most of the first draft - I think it's all the education writing I've done, where they give you about 3 months to do a non-fiction title, complete with research.
Jack Dann once told me that you always have to "hustle" for writing jobs. He was right. I have been hustling for projects for years now. I watched him at work once, his ears pricking up when I introduced him to my then-publisher, his hand reaching into his pocket for a card... Whether I will ever be as successful as he is, I don't know. I doubt it. But you don't have to be a massive bestseller to be able to consider yourself a professional writer. If you "hustle" and get work, if someone is prepared to pay you to write for them, you're a professional writer. I've found it pays not to be fussy - fiction or non-fiction, juvenile or adult, if someone is buying, I have a go. And while I'm establishing myself and letting my name be known to those who are buying, I can still get on with the SF and fantasy that are my first love. I've sold a few of those stories too!