Desire is the motive energy behind all action.
When doing a character bio the trickiest thing to do is to create an area of misunderstanding or misguided belief in your protagonist, (the one who changes the most) and in your antagonists (the characters who obstruct, impede, challenge, love, hate, and generally impact the protagonist.) It means you have to know the difference between what they actually need, and what they believe they need.
If a character is motivated to act because he is “barking up the wrong tree,” then this will cause him to act, but soon he will realize that the antagonist blocking him from getting what he wants is precisely why he must re-evaluate what it is he wants. If he can get closer to that core truth about what he really wants, then the action will be ramped up a notch. The desire will increase to obsessive desire. This is where audiences witness character change through story. The ramped up desire also increases narrative drive, which in turn increases conflict. This “barking up the wrong tree” is the basis of all desire in your characters, and desire is the motive energy behind all action.
The main character will also think: What will happen if he doesn’t get what he wants???
In books (and to a much greater extent in movies) the protagonist’s obsessive drive is wanting something more than we do. In our lives we make compromises. We usually follow the path of least resistance because we can’t endure the conflict. We generally want easy lives. In stories, characters want stuff so badly that they actually go about getting it, doing whatever it takes to get it, in ways we probably wouldn’t.
If a protagonist doesn’t want something badly enough, he or she won’t do anything about trying to get it, and then there won’t be any story!!