Inside the writer brain

One reason I don't outline much is that, even when I think I know what's going to happen between characters, I can't be sure until I start writing the scene.

The scene unfolds moment by moment, each character reacting to what has just been said or done by the other. It's a balance between Where do I want this scene to go? and What would this character naturally do in this situation?
 
Let's say I have a scene where Character A has wronged Character B, and is now apologizing. I think B will forgive A, and I want that to happen for plot reasons. If I were writing an outline, this scene would be labeled, "A apologizes; B forgives."

But when I get into the scene, A is not contrite enough, or not patient enough. Or B is too hurt. Their dialogue is not going where I thought it would. I realize that if B forgives A right now, it will come off forced. Readers--in this case, myself included--will think What's wrong with B? Why did B cave like that? I don't buy it.
 
Then I have a few choices:
How fixed are A's words and tone here? How sorry is A, anyway? Can I make the apology easier to accept?
Can I move this scene to a later point, so that B will have more time to cool off, and forgiveness will be natural?
Maybe B shouldn't forgive A after all. What happens if I go down that road instead?