I love it when characters surprise you, just like real people. When I write a scene I just try to make the characters behave in a way that feels natural to them. Sometimes that means they make a left turn and do something unexpected. Those are always the best scenes in my opinion.
Before I do anything, I think, well what hasn't been seen. Sometimes, that turns out to be something ghastly and not fit for society. And sometimes that inspiration becomes something that's really worthwhile.