In commercial fiction especially, everything in the story usually contributes directly to the plot The shorter the story, the truer this is

What characters do must grow out of who they are, and who they are is, in turn, influenced by what you make happen to them.

You think intelligence and grit can succeed by themselves, but I'm telling you that's a pretty illusion.

Changers are characters who alter in significant ways as a result of the events of your story. They learn something or grow into better or worse people, but by the end of the story they are not the same personalities they were in the beginning. Their change, in its various stages, is called the story's emotional arc.

Characterization is not divorced from plot, not a coat of paint you slap on after the structure of events is already built. Rather characterization is inseparable from plot.

Some writers find that they don't know their themes until they've finished the first draft (I am one). They then rewrite with an eye toward balancing on that tightrope: not too contrived, not too rambling; does what I'm saying about the world below me actually add up to anything? Other writers pay attention to these things as they write the first draft. Either way, an awareness of the macro and micro levels of theme can provide one more tool for thinking about what you should write, and how.

In commercial fiction especially, everything in the story usually contributes directly to the plot The shorter the story, the truer this is