NPCs can grow and change—but hopefully not easily.
discusses techniques that, when applied, give an NPC a Character Arc.
Quite often in a film, one or more characters have something wrong with them. More specifically, they start the film with what I call a fear, limitation, block, or wound (FLBW). For example, they:
Are a coward.
Feel guilty over something they've done.
Have low self-esteem.
There are a vast array of possible FLBWs.
Let's say the character's FLBW is that he has no idea who he really is as a person. He might have felt this way all his life, or maybe some devastating experience happened to him last ...