Characters should change over the course of the story. This is known as an “arc”, which you and me should really already know, but if you read some of my initial drafts you’d be forgiven for thinking I was writing for AVATAR, where NOTHING CHANGES AT ALL. Even if they ultimately return to their original state, the ride between should be up and down if there’s to be AWESOME CHARACTER DRAMA!!!
In planning, write the name of each main character. Describe each of them in terms of their personality at the start of the story. Then describe each of them as they are at the end. What they’ve learned and how they’ve changed.
If you can’t do this, your characters need work. (You moron, John.)
I may refer to this in future as the Harry S. Plinkett Rule, after the brilliant “describe the characters in THE PHANTOM MENACE without using their physical appearance or role” part of the equally brilliant 70-minute Phantom Menace review.