Audiences empathize with the hero, so whatever experiences the hero goes through, the audience can go through those same emotional ups and downs. One way to keep your audience and your hero going through an emotional roller coaster is to teach your hero a lesson.
In the beginning of your story, the hero represents the opposite of your theme. By the end of your story, the hero has changed to embrace your theme. In the middle, the hero first learns about the theme and realizes that his or her old way of life can never be sustained. Because your hero changes over the course of your story, the hero learns a lesson.
In “A Clockwork Orange,” the hero is a gang leader who thinks he can do whatever he wants to others. When he’s finally caught, he agrees to go through an experimental procedure that will force him to be good. However, that conditioning essentially robs him of the choice to decide whether to be good or not. That inability to choose makes him an easy target for all his previous victims to turn around and torment him. Finally at the end of the story, the hero regains the ability to choose again, and that’s when he realizes that the choice to be good or bad rests solely with him.
In “Liar, Liar,” the hero thinks he can lie his way through life. By the end, he learns that he has to tell the truth because telling the truth can get him what he wants as well. From start to finish, the hero has learned a lesson.
In your screenplay, make sure your hero learns a lesson. The beginning and ending of your story must show opposite extremes of your hero to create change. The bulk of your story is about teaching your hero how to change.
In “Monsters, Inc.” the hero is a monster who specializes in scary little kids to capture their screams that power the monster world with electricity. The hero’s lesson is to learn that scaring kids is wrong, but making them laugh is much better.
Think of any of your favorite movies and chances are good that the hero learns a lesson along the way. In the beginning, the hero is stuck in a dead end life and by the end, the hero (and the audience) has learned an important lesson which is related to your theme. When both your hero and your audience feel they’ve learned a lesson, then you’ll have created a compelling story.