I continue to be amazed by Hugh MacLeod's How to be Creative series on his Gaping Void weblog. His most recent contribution is this gem:

15. The most important thing a creative person can learn professionally is where to draw the red line that separates what you are willing to do, and what you are not. Art suffers the moment other people start paying for it. The more you need the money, the more people will tell you what to do. The less control you will have. The more bullshit you will have to swallow. The less joy it will bring. Know this and plan accordingly.

Hugh is the guy who draws cartoons on business cards. Though I love the one that accompanies the post, the one here has this bit of wisdom, "If an ordinary person can understand what you do, you're already half way to becoming a commodity."