The thing about stories — especially in Western culture — is that the main character is expected to have agency. They’re supposed to make decisions and take action, not just have things happen to them. Sure, the inciting incident can happen to them, but after that? Not so much. (Well, except the bad stuff, but getting out of it? That’s on them.)
However, you can take this to the next level!
If you want your story to be more realistic, there’s something even harder to remember — secondary characters have agency, too. They have their own hopes and dreams and emotions — that don’t necessarily revolve around the main character or the main plot. And? Throw-away characters that only exist for one scene? Can have agency — or at least external motivations.
You hear a lot about ‘white room syndrome’, where writers forget to describe the setting. But, there’s a related thing I’ve talked about before of forgetting about characters that the main character isn’t actively interacting with — basically just shoved in stasis and pulled out when the main character needs them again. With no growth or change possible.
Additionally? Characters need to be individuals, not just defined by their roles. A couple days ago, there I am, taking a shower, when I realize that a soldier’s reaction from the end of the manuscript I’ve been querying for a while now — is wrong. The main character’s from a small town, thus when she encounters the soldiers from that town, they’re not going to react like strangers — which I figured out several edits ago. But, not all soldiers are going to react the same way, and some might be as horrified as the main character about [spoiler].
You need to do your best to make sure that all your characters are three-dimensional — not just stereotypes or defined by the plot-role they’re fulfilling. It’s easy to plunk in the spunky brunette English-major barista at the Barnes and Noble café, what about a single-dad, or the immigrant who’s teaching themselves English on their lunch breaks, or the female combat veteran who lost a leg? It’s a lot more interesting — and realistic — when even background characters are written with a touch of nuance rather than plucked out of central casting.
Have you read any novels with boring background characters straight out of central casting?
Who are your favorite three-note background characters you’ve read — or written?