Some people fondly think that once you decide what a character's motivation is, it becomes encased in concrete and can't change.
Sometimes there is a better or stronger way to have a take on the same subject.
A case in point is my upcoming Online Serial -- His Stand In Bride. I had written it and thought I knew the motivation. The editor read it and my short synopsis and asked for revisions. The heroine's motivation wain the synopsis was at odds with the story and wasn't strong enough. In fact, she thought my heroine was intelligent enough to appreciate the irony of the situation. Would I mind threading through a different motivation -- namely a belief in the right to choose one's destiny as that was what she was getting from the story. For those curious amongst you, I had thought the heroine's motivation was a belief in true love. And of course, being an editor she was absolutely right. I think the story is much stronger.
This probably shows that I over simplify my character's motivations when I write a synopsis or a detailed background note. Also complex characters will have complex motivations. Some of the motivations will not be revealed to the author until she is in revisions or has the first draft done. And sometimes she may think that she has threaded the correct motivation through only to discover that there is another deeper reason for the behaviour. Characters can be tricky and hide things even from their creator.
Nothing is ever written in concrete and there are different ways to see the same thing. And Debra Dixon's book on GMC made me freeze solid. I prefer other books on the craft of writing and ways of looking at things. And that is fine. The only process i have to worry about is my own.
What matters is that you get there in the end and create a page turning romance.