Character arc
A character's trajectory of transformation between a story's start and end — what they believe, become or refuse to become.
The character arc describes a character's transformation across the story: the coward finding courage, the idealist corrupted, the cynic learning to believe again. Convention distinguishes the positive arc (growth), the negative arc (fall) and the flat arc — the character doesn't change but changes the world around them (recurring detectives, moral figures).
The deep mechanism rests on an initial lie: the character believes something false about themselves or the world, and the story is the machine that forces the confrontation. Plots that "run on empty" almost always suffer from a missing arc: events occur, no one is transformed by them.
Example
Ebenezer Scrooge: from miserliness to generosity in one night — the archetypal positive arc.