I think there comes a time in every writer's life when they realize their characters are more real than they seem. For example, I have a book that I had the entire timeline for. I knew which events had to happen when, and life was good. Until I made the mistake of getting a very outspoken character involved. She waltzed right in and said, "You know, I think I'm going to move things around a little." We had a bit of an argument, which she won, and she proceeded to change things around while I sat in the background going, "But I though I was the author!!" I've been very careful with her since then. :)
There are other ways for a character to become more real, however. Recently I've been dealing with a character who has a lot of emotional baggage to deal with. Suddenly, all by herself, with no push from me, she decided to grow up a bit. I hadn't planned it, but as I wrote, I definitely felt her learning her lesson and saying, "Okay, yeah, I can do this." These are the moments that make it worth being a writer.
Or they may be the moments that tell you I'm crazy! Your choice!
Fare thee well, friend!