There's a basic structure to almost every movie you've ever seen. It doesn't matter if the movie you're watching is Killer Klowns from Outer Space or 3:10 to Yuma or Kung Fu Panda. It doesn't actually matter if it's The Godfather or a commercial for laundry detergent. There's a common structure there. It's present in 'serious' indie stuff and Disney films (and their spoofs).
Why is the structure there? Because people expect it. It's a chicken and egg thing. It's vaguely disturbing how prevalent the three-act structure is. If I were in a better mood, I'd find it endlessly fascinating just how productive this structure is. I'd wonder if humans weren't hard-wired for this story structure. I'd go on and on about how formulaic films do everything they can to fit into the structure, while more challenging films merely use the structure to help create new and better story. But it's been a long week, so it's just vaguely disturbing right now.
What is this structure, exactly? You can find a description of it in Aristotle's Poetics. You can find reams of paper written on the hero's journey, the writer's journey, George Lucas' journey. Syd Field will bisect the middle act, and make three acts into four. Individuals throughout history have produced incredibly insightful and careful analyses of the basic story structure that has fueled drama and literature for as long as we've existed.
If you're not up for a big research project right now, let me sum it up for you. Your hero walks carefree and/or miserable through the equilibrium of his life until wham -- something throws everything out of balance. The hero reacts indignantly -- as any of us would. But things get worse -- he can't get away from the plot. Just has to power through. Things start looking up -- our guy even learns a bit about himself -- but it lasts just long enough to find a bigger problem. "Hey -- here's something I didn't know I could do!" he thinks. And of course, he can't actually do it. It's all going to hell now. The train's riding down the tracks, the alien forces are massing overhead, or you find yourself facing a debate in front of 100 million people right after humiliating yourself with a transparent political stunt. But lo and behold, you learn how to escape what got you into trouble in the first place. You overcome it. You gain knowledge. You gain love. You gain That Which Means Most to You. Or, in some dreadful cases, you don't.
How does this all fit together? Well, the character is usually constructed from two main elements: the goal of the story and the inability to reach that goal. That inability is usually neatly summarized as a flaw or misbehavior. Even in fairly complex characters there's one main defining trait because it helps the audience recognize the character.
Now why on earth would that appeal to human beings? Like it or not, we're all tied up with our own misbehaviors and desires. We're tied up in our own cycles. We usually are responsible for these cycles because of some behavior we can't get past. We drink too much. We surf the web too much. We avoid conflict, or race toward it. We're bullies, or we're wimps. We've got a basic nature, and that means the stories we experience tend to repeat themselves. Every Tuesday afternoon I teach for six hours. Every Tuesday morning about 10 AM I'm frantic with worry about what I forgot to do. Every Tuesday at 10:15 I remember it's eating and bathing that I've forgotten. At 10:45 I'm running out the door to catch the train. It doesn't matter how much I plan. I'm bound to do it.
Think about it.
There's something hugely cathartic about people escaping their cycles. Watching others do it is powerful. It's rare in real life. But it's a gorgeous thing when it does. Maybe that's all movies are really about.