When a movie runs out of surprises, it runs outs of interest. To keep audiences interested in your story, you need to keep them surprised.
Now surprises don’t mean random events occurring for no apparent reason. Instead, surprises need to be carefully set up ahead of time and then unleashed at the proper time so it’s not only a surprise, but also makes logical sense when it’s finally revealed.In “Die Hard,” Bruce Willis discovers that the terrorists have dynamite although he can’t figure out why. First, he uses this dynamite to blow up two terrorists manning an anti-tank gun that’s shooting at an armored SWAT vehicle. Second, he discovers the terrorists have rigged the dynamite to blow up the roof. That\’s an example of a surprise. What seemed out of place initially (the dynamite) suddenly takes on a more sinister meaning.
One way to surprise your audience is to hide the villain’s true goal until the last minute. In “Die Hard,” the villain’s mystery is how he plans to rob the building and escape. When we learn that he plans to blow up the roof with all the hostages on it to create a diversion so he can escape, that’s a surprise.
A second way to surprise your audience is to keep the hero’s goal hidden. In “The Terminal,” Tom Hanks plays a stranded foreigner stuck in an airport. We don’t know why he’s there but we see hints of him holding a strange can. Later we learn that he came to New York solely to get an autograph of a famous musician for his father and the can contains the autographs of other musicians.
By stringing out both the villain and the hero’s mysterious goals, we’re kept in suspense and ultimately surprised at the end when we learn the true meaning. Movies that fail to hide the villain or hero’s goals tend to get boring real fast and reduce themselves to lots of action that goes nowhere just for the sake of action.
So when you’re writing your screenplay, hide your villain’s goal and your hero’s goal. Then tease out hints of both goals over time until the end when you finally release the surprise on your audience. By planting subtle hints along the way, your surprise will be a surprise and not really a surprise, which is the most satisfying surprise of all because audiences will suddenly recognize what they should have guessed all along.
By keeping elements of your story hidden for a surprise near the end, you force the audience to play detective and actively stay involved in your story to figure out what all these subtle clues mean. By the time the audience figures out what the hero and villains’ mysteries are, Act III rolls around with pure action so now the audience can sit back and watch the final battle with full understanding what’s happening.