Characters who have their own minds.

Isn't it extraordinary how you think you know your characters inside out and you are walking with them as you guide them through your story. But then they suddenly turn around and stare at you with their hands on their hips saying: 'That is not how it is. I would not do it like that. In fact this is who I am.'
I had an incident like that today with one of the female characters in the PhD novel. I am telling the story using four voices, Ben - who is probably the main character but also Matt, Millie and Amna. They take it in turns to have a chapter allocated to them. Today I was writing from Amna's point of view and I thought I knew her well.
But oh no, did she take me by surprise. She took every preconception I had about her and ripped them up by telling me something that has put a whole different spin on her story. It is something that I hadn't even considered. But she had and she wanted it said out loud. So that's what I did.
Now if you are writers you will know what I am talking about, if not you will now be totally sure that I am round the twist, which is also possibly true.