Transformation

Ultimately in any story, the hero or main character must be transformed in some way or the whole journey would not have as much meaning. He or she must overcome a fear, gain a previously unknown strength or skill, or change in some way (usually for the better) as a result of the events and situations that are encountered.

(The exception to this is serials or sit-coms. In these cases, the people cannot change or the show would be over.)