Occasionally I’ll be writing a new character into a story and they’ll force themselves further into the plot until they’re no longer a character with only a scene or two and few mentions to their name.
A blacksmith in my current novel worked her way into more screen time and even had time to fall in love. Some of these characters have the ability to change my plans without my say. Sometimes it gets a little annoying, but most of the time it actually helps the story along.
Some characters truly live inside your head and have a mind of their own, it’s how you know they’re realistic and interesting, as they do things that change the original content you wished to write. As a writer, you just need to be able to figure out how to give the character the time they need without straying too far from the plot you’ve laid out before you.