I have often heard writers say that while they were writing, thinking they were going in one direction, their characters took on a life of their own and insisted on going another way. I barely believed it, myself....that is until last week.
There I was, convinced I knew the reason that my character behaved the way she did, when all along she had a secret that she kept from me. It came out, as a total surprise, in a conversation she was having with her daughter. It put a whole new slant on her behavior and explained better than I ever could have why she felt guilty and depressed. (And no, I am not going to reveal it here. You will have to read the story and be surprised.)
The thing is, it made the rest of the story flow so much more easily. I won't say it wrote itself, but I did complete the story quickly, and I like the result.
I don't think I can force my people to "take over," or reveal a hidden truth. But if I try to really know them, to be true to their lives and their characters it may happen to me again. I would be very happy with another surprise.