Functional Flat Characters

 I’m a big fan of character development. In my opinion, it’s the best way to get the audience drawn into the story—if you’re emotionally invested in a compelling character, their conflicts become important (and conversely, audiences will bail on complex plots if the characters are dull or off-putting). And I'm not the only one. Pretty much any source of writing advice will tell you to make sure your characters are complex and developed, and to avoid the dreaded 'flat character'. That said, you do not have to develop every single character equally. One of the big factors is audience expectations and attention. Readers are alert for details of character development which hint that this seemingly innocuous person or unicorn or Vulcan is actually an important player. Give all your minor characters a lot of backstory and the readers will get frustrated by the overload. If a character is really just a bit part—the annoying bureaucrat who’s keeping the protagonist from bringing a critical parcel through customs, the jolly bartender who innocently passes on plot-critical information, or the snooping little kid who is the ‘spanner in the works’ and reveals the protagonist’s hiding place—it’s okay to write in a one-note person. It signals to the reader that we won’t be seeing them again. On a note of caution, however, it’s important not to have the bit part character’s existence revolve around the protagonist. By that, I mean that they should have their own motivations, however simple, and not exist to shill the protagonist or sacrifice their life after knowing said protagonist for five minutes. Sure, they're on the reader's radar because they're interacting with the main character, but that doesn't mean they should be the same in-universe. Let them walk on, intersect with the heroes, and get back to their own lives.