So you’ve got your protagonist. And your antagonist. And your protagonist’s best friend. And your protagonist’s girlfriend. And your protagonist’s best friend’s girlfriend. And your protagonist’s best friend’s girlfriend’s cat. And your antagonist’s brother. And your antagonist’ brother’s girlfriend… You get the idea.
Do you really need 99 different characters, most who only play a tiny part in one scene, all who must be tracked throughout revisions with “Did I change that eye color/hair color/name/spelling/age/gender etc.?!!?”
No. Your story needs maybe a handful of characters who the reader will care about, characters who will earn the reader’s love or hatred, who will enrich the story from start to finish and enthrall readers.
An example of this unfortunate occurrence is the bestselling Warriors series, which is about wild cats. Don’t get me wrong, I love these books. But there are way too many characters–around sixty is my estimate. There’s an important character whose eye color changes three times throughout the books. There’s a minor character who changes from male to female. Um, okay, but I’m pretty sure sex reassignment surgery hasn’t been developed for cats yet.
You will think of new characters all the time. That doesn’t mean they’re automatically the next big thing that will spice up your story. Before letting them join in, make sure they belong there.