Creating the Moral Need, John Truby, The Anatomy of Story, p. 42
Writers often think they have given their hero a moral need when it is just psychological. Remember the simple rule of thumb: to have a moral need, the character must be hurting at least one other person at the beginning of the story.
Two good ways to come up with the right moral need for your hero are to connect it to the psychological need and to turn a strength into a weakness.
In good stories, the moral need usually comes out of the psychological need. The character has a psychological weakness that leads him to take it out on others.
To give your character a moral as well as a psychological need and to make it the right one for your character,
Begin with the psychological weakness.
Figure out what kind of immoral action might naturally come out of that.
Identify the deep-seated moral weakness and need that are the source of this action.
A second technique for creating a good moral need is to push a strength so far it becomes a weakness. The technique works like this:
Identify a virtue in your character. Then make him so passionate about ir that it becomes oppressive.
Come up with a value the character believes in. Then find the negative version of that value.