Here is an excerpt from my book Savvy Characters Sell Screenplays!:
A WINNING SCREENPLAY: STORY = PLOT = CHARACTERS
Story generates plot; it informs what the narrative is about. The plot informs how the story unfolds. And it is your riveting characters who must inform and drive your plot forward.
CHARACTERS = PLOT
Who will live? Who will die? How will they survive?
Who will win? Who will lose? How will they win? How will they lose?
Who will succeed? Who will fail? How will they succeed? How will they fail?
Who will find love? How will they find love?
These aforementioned generic movie taglines, emphasize the significant word “who”— your characters.
To create a believable and compelling plot, your characters must be fleshed out and their distinct characterizations (motivations, behavior, attitudes, and so on), must be gripping and plausible in order to drive the plot forward. When you try to get characters to do what the plot determines, then your characters’ actions, behaviors, and motivations will not be realistic, and they will read as false and contrived.