|She's a little bit rock 'n roll, he's a lot country.|
Ideally, your focus will be on the character who has the furthest to grow. The one who has the greatest odds stacked against him. The one with the most to lose. The one with the most relatable wound.
How do wounds happen to characters? Well, how do they happen to us? In one of two ways: passive and active. Passive would be if a forest fire burned your house to the ground through no fault of your own. Active would be if you were the one playing with matches in the woods. Either way, you'll wind up a changed person. However in only one of those examples does the situation paint a more complex, detailed picture of a character.
Either way, if your house burns down, we can learn a lot about you. What do you prioritize? Who/what do you save first? Do you shake a fist at the skies? Do you start rebuilding immediately? But a character who inadvertently burns down her own house instantly has us asking questions. She immediately invests us. Something's wrong. She's troubled. And the best stories are about troubled people becoming people in trouble.
To boil it down simply, the flaw creates the wound. A character's defining characteristic directly causes the inciting incident. In the beginning of your story, your protagonist digs themselves into a mighty hole with a backhoe, and the bulk of your tale is you handing them an olive fork to dig themselves out.
In The Social Network, Mark's flaw is that he's status-obsessed. He creates the wound by demeaning Erica at dinner. She leaves. He spends the rest of the film trying to recover her.
In Finding Nemo, Marlin's flaw is that he's overprotective. He creates the wound by demeaning his son at school. Nemo's abducted. Marlin spends the rest of the film trying to save him.
In Dallas Buyers Club, Ron Woodroof is a homophobe who believes himself invincible. His fast and loose 1980s lifestyle leads to his contraction of HIV, and he spends the rest of the film trying to save his own life as well as the lives of all those infected.
In Casablanca, Rick's broken heart threatens to put Ilsa and Laszlo into unspeakable danger. He spends the film working his way through his bitterness to ultimately make the right decision at the key moment.
In Jurassic Park, Alan Grant doesn't like kids (to an extreme). Then he's thrown into a situation wherein he must save two of them from becoming dinosaur chow. At least one of the children ends up saving his life in the process, and by the end of the film he has a child under each arm, sleeping up against him. Who'd have thought?
Bottom line, your character, by virtue of who they are, must land themselves into huge trouble. By virtue of who they can be and should be, they pull themselves out. When who they are turns into who they can be, their potential, there's your story.