One of the hard and fast rules of scriptwriting comes in the form of the 'Character Arc.' During the course of the story, the protagonist undergoes a journey of some type which during so allows her/him to change from what they were to 'something else'. Generally it's a spiritual, moral or sometimes a physical transformation from a person of lesser understanding/capability into someone (or something) with a wider scope or greater capacity. Now here's the thing, just as 'Morpheus' said in the Dojo Scene of 'The Matrix', "Some rules can be bent, others can be broken" that same approach to scriptwriting can be applied to character arc.

Here's a pretty good breakdown concerning 'bending' the rule on character arc by Brad Johnson of Script Magazine:
Specs and the City: Character Arcs (or the lack thereof) and 'The Fugitive'