I know I'm not the only person that deals with this. I just feel like complaining... I started having trouble with a character being overly hostile. When I complained about it to my family, I was told to just make the character behave. I wish.
Non-writers seem to be under the impression that writers control their characters. For me, it's more like I rent head-space to my characters. Except I don't actually get the benefit of collecting rent.
When I was dealing with this particular character, I had intended for her to be rude, but the intensity of her behavior was unexpected, and told me there was more to it. So I took a day and explored why she was behaving this way. What I got at the end of the day was her character arc. It was important for me to know, even if what I actually wrote gets scrapped.
This is why I don't bother getting too detailed with my outlining. Things go off on tangents too often and I would have to scrap half of my outline. It's what works for me.
Before that I had a side character decide to tag along for the whole adventure...and become the love interest. I was not planning on including any romance in this story, but he's not going away. I'm trying telling myself that it helps add to the conflict.
So...only a week into NaNoWriMo and things are spinning out of control nicely. I've come to the conclusion is that if the characters are behaving perfectly, something is wrong.
More about NaNoWriMo?
Four Benefits of NaNoWriMo
NaNoWriMo Prep Time
What I Did To Silence My Inner Editor