Movies without a theme tend to be directionless and short-sighted where every scene tries to do something, but without the unifying goal of a theme, each scene fails to support the others. You can see this in bad comedies where each scene tries to be funny, but there’s no overall theme that unifies the humor. As a result, the comedy isn’t that funny and the story isn’t that good, which creates a flop.
Typically themes are simple like “Women are second-class citizens in a man’s world” (Thelma and Louise) or “You have the power to change your future” (Back to the Future). However, another way to look at your story’s theme is to pose a question. In “Terminator 2,” the theme is that killing is wrong. Yet if you rephrase this as a question, you might get “Can you solve problems without killing?” Then as you watch “Terminator 2,” you can see that it keeps answering that question with a yes.
In “Thelma and Louise,” you might rephrase the theme with the question “Can women survive in a male-dominated world?” Then each scene shows how women struggle against men.
By thinking of your theme as a question, you can flirt with the pros and cons of your theme. Your hero represents the pro side of the question while your hero represents the con side of the question. In “Terminator 2,” the hero (the good Terminator) gradually learns that killing is wrong. Yet the villain (the liquid metal Terminator) never learns this so he eventually gets killed in the end. Your hero succeeds because he changes. Your villain fails because he fails to change.
Both your hero and villain are so similar that they may start at the same place related to your theme. In “Terminator 2,” both the hero and the villain think that killing is an acceptable way to solve problems, but only through the guidance of a mentor does the hero change and learn a new way of living.
All great stories are really morality plays that teach a lesson. That’s because all primitive stories also explained the world around them from how the leopard got spots to why cats chase mice. Such primitive stories help explain the world around us and movies are no different. A movie without a theme simply tries to entertain us. However, a movie with a theme not only entertains us, but teaches us a lesson while entertaining us. The theme makes the entertainment stronger and more unified. To see the difference, just watch “Terminator 3” for its lack of a strong theme and its emphasis on trying to entertain us with action and special effects. “Terminator 3” simply fails despite making a lot of money.
So what you want to do with your story is think of a strong theme that explains something about life while phrased as a question. Then your story can use your hero and villain to answer both sides of that question. When you get stuck writing, just think of your theme and ask how your next scene can answer your theme’s question, and that alone should help remove a lot of confusion and doubt that creates writer’s blocks.