The main character of every story SHOULD change just a little bit by the end of your book. Whether that means emotionally, mentally, or physically changed, some change should happen.

Static vs. Dynamic Characters
Static: Characters who don't go through a major change in the story.
Dynamic: Characters who go through a change at the end of the book.

*EVERY MAIN CHARACTER SHOULD BE DYNAMIC*

Ways your character can change are either through a positive or negative experience. No character suddenly changes if nothing happens.

Flat vs. Round Character
Flat: A character who only has one main personality trait.
Round: A character who has many different personality traits.

*ALL MAIN CHARACTERS SHOULD BE ROUND*

The reader would be a lot more interested in your main character if he/she had more than one trait.