One of the thing a lot of writers will tell you is that their characters seem to have minds of their own, taking over the story and refusing to do what the author wants them to. I don't know if this is because we're trying to make our characters do something...out of character or if it's some fault of our own, but it is both exhilarating and frustrating at the same time.
This just happened to me the other day with my current work in progress. It's a romantic fantasy with two brothers who each have different magical abilities, inherited from their nature-spirit ancestor. Aeran, whose supposed "gift" is the ability to know and affect what others are feeling, who is normally sensitive and cautious and careful with other people's feelings, reacted to the heroine with knee-jerk hatefulness.
His behavior shocked me--and his brother. But when I went back and thought about it, his past, his occasional difficulty with his temper, and his mood and situation at the moment, I realized it made sense. I'd been trying to force him into an unnatural equanimity, an even-temperedness no one would be able to maintain.
I think things will be tense in that house for a little while, even though he's properly repentant and she's quick to forgive him. Old grudges are hard to shed. If enough people clamor for it, I'll post an excerpt next time it's my turn.
Countdown to Speechless (my forthcoming book from Cerridwen Press): 2 months and 2 days