A Character Arc Doesn't Come Easily to a Character
A Character Arc is the rocky path of growth a character undergoes, usually unwillingly or with difficulty, during which the character wrestles with and eventually overcomes some or all of a serious emotional FLBW.
The character is unwilling to grow because it's tough to grow though a FLBW. Usually, the character has created a life in which his or her FLBW doesn't get in the way.
For instance, if the character lacks ethics, his life is fixed up at the beginning of the story, in a way so that he can get away with his unethical behavior without consequences. Perhaps he has an entire system of cover-ups and excuses to explain where he is and what he's doing when he's really off doing something unethical.
Another example would be a shy person who has gotten himself or herself employed in a job or even a field where interacting with others isn't required.
And then something happens to the character. He or she falls into a new circumstance or an adventure or simply a change in events, and now that FLBW gets in the way all the time. The character is forced to grow, like it or not.
As I mentioned, going from "not knowing who you are" to "knowing who you are" is the Character Arc that Luke Skywalker undergoes in Episode IV.
Luke is forced to grow due to the new experiences he undergoes, such as:
One of the key factors that makes a film or other story emotionally gripping is watching one or more of the characters struggle through their fear, limitation, block, or wound.
It's not easy for Luke to become who he is. It's not easy for Princess Leia to learn how to love. It's not easy for Han Solo to learn how to go from being an outlaw loner with just a sole friend in the world (Chewbacca) to being an ethical team player. It's not easy for Obi-Wan to "get back in the game." (When we meet him, he's living by himself in a cave, doing nothing to fight the Empire.) It's not easy for C-3PO to learn courage.