on Helping Writers become Authors:

When it comes to creating memorable, emotionally resonant characters, your character’s personality may seem like it’s just a “flavor,” but in many ways it’s actually the foundation of the story itself. Your character’s personality influences everything: the character arc, the voice in both dialogue and the narrative (if the character has a POV), and the goals that shape your entire plot.

In many ways, your characters’ personalities can determine whether or not the story works. This is most obviously true when it comes that special “it” factor that creates unforgettably quirky or nuanced characters, but it’s even more true when it comes to the cohesion of your story’s deeper workings—where character, plot, and theme all come together.

In short, understanding personality might just be one of the most powerful tools in a writer’s toolbox.