Well, I pretty much experienced that my characters have their own mind. I wrote a story once, which had absolutely nothing to do with Lois and Clark. In this story I needed a supporting character who was only supposed to take the main character to a certain place. And when I made him walk into the scene, he suddenly decided that he didn't want to be a supporting character. Out of the blue, I had a whole new main character in my story.
I have to admit that this kind of character action is pretty useful when you are stuck and your characters decide to help you in that situation
