It happened to me last fall for the first time. It takes a lot to push me over the edge, but the client was so offensive to me that I knew I couldn't represent her in good faith to get her the work that she wanted. She kept pushing me to do things that weren't in her contract and discounted all the work I had accomplished for her. In addition, I didn't feel aligned with her ethics. Better for both of us to be done with the relationship.