|"I hate people. But I adore these window dressings."|
It's the difference between, "An octogenarian wants to move his house to Paradise Falls" and "A cantankerous but good-hearted octogenarian wants to move his house to Paradise Falls to keep a lifelong promise he made to his late wife: a promise he believes he broke."
To put it simply, if your story is only about the plot, then you're doing it wrong. Your story must be about the characters. Their actions (or inactions) are what set the plot in motion. Your characters are what make the plot engaging. When people ask you what your story's about, start with the characters.
There's a difference between saying, "It's a film about a dinosaur theme park" and "It's a film about people trapped in a dinosaur theme park." Going even further, Jurassic Park tells a lot of stories, but focuses mainly on Dr. Alan Grant (Sam Neill). He goes from a guy who threatens children to one who lets two kids fall asleep on him. He transitions from bully to protector. It's fun to watch dinosaurs eat people, but the film is a success not because we care about how many people the dinosaurs eat, but because we want to see Dr. Grant, the guy least likely to go out of his way to save a child, protect little Lex and Tim and make it out alive.
A prominent paleontologist who doesn't like kids must protect two children from certain death. That's Jurassic Park without a single mention of dinosaurs. But at its heart, it's what the film is all about. It's why the film isn't simply a two-hour montage of dinosaurs doing their dinosaur thing.
Troubled people to people in trouble. Your character must be a train wreck in some way, shape, or form. In previous examples, I've touched on Finding Nemo's Marlin, The Social Network's Mark Zuckerberg, and The Shawshank Redemption's Andy Dufresne. They all wind up in trouble, but you'll note that it's because in each case, they're already troubled.
Marlin's overprotective to a fault. Mark is status-obsessed. Andy isn't good at expressing himself. Each of these personal troubles drop their respective character into hot water, which becomes the plot. Your characters' own troubles, quirks, psychoses, and so on, must be front and center: their defining characteristic.
To create a successful story, your characters must be messed up.
Look at Paul Anderson's remarkable script for There Will Be Blood. Daniel Plainview (Daniel Day-Lewis) is a loner. He's estranged from his family. He's hinted to be impotent. He has a violent temper. He has a very soft spot for children. He's really messed up. He's really complex. And he's impossibly fun to watch. You can't turn away from this guy. He's the sort of character that actors want to play, the sort of character who, if well-played, could easily net someone an Academy Award. Who he is informs what he does, which thenceforth drives the story.
The fact is: audiences love a train wreck. The more of a paragon your character, the closer they stretch to perfect, the more boring they are. Characters who are a mess of issues, self-doubts, and self-conflict, are endlessly fun to watch. Audiences love a struggle, and it's fun to watch messed-up people struggle out of messed-up situations.
It reminds us of ourselves.