The outline calls for this character to get angry at another major character at this point. He's done some crappy things, disappointed her, let her down; she should be angry. In fact she needs to be angry and kick him out, so he can go and [blah blah more plot follows]. So, I start the scene; he shows up, acts sheepish; I try to write her being angry... She won't get angry. She's confused, she's hurt, she asks questions... she's just not getting mad. Everything he's saying is pushing her in a different direction.
Well... everything he's saying is true to his character. And how she's reacting is true to hers. She's a sweetheart, a pushover; she's the character who takes care of everyone and cleans up all the messes. But dammit! She can't do this! If he doesn't go and [etc etc], then the whole ending falls apart.
Finally, I stopped and listened to them. They know who they are; they know what they're doing. I thought about it a bit, and finally figured out that they can go on as they are, I can adjust the outline; he can leave anyway and do the things the book needs, and the reason he now leaves is going to make even more sense, I think.
You don't know the characters when you write the outline. I mean, you sort of do; you invent them, after all. But they're a paragraph from your imagination at that point. Now they are 400 pages of action and thoughts and crappy decisions and love and drama and *living*. They are alive and real, and they don't like being pushed around any better than the rest of us do.
In other news: I love my friends, and I love reading my friends' books. I'm so lucky that my friends write such fantastic books.
But... sometimes, perhaps, I should give more thought to the order in which I read books. I just finished maryrobinette's truly delightful and riveting Shades of Milk and Honey, whereupon I dove right into Mira Grant's (aka seanan_mcguire)'s fascinating, razor-sharp Feed. The horrible screeching sound you hear is the gears grinding in my brain, as I adjust to the nearly-annihilatingly-total change in tone, setting, and subject matter. :-)
Five chapters in; I think I'm okay now. But, wow.