Luke was cocky and immature. He never once thought he would lose to Vader in Empire until he had been bludgeoned repeatedly, had his hand cut off, been disarmed, and backed onto some precipice from which there was no escape.
Before all that, he was like yeah. I’ve got the Force man. My father was a Jedi and I’m a Jedi too. I’m going to go and avenge him because I’m the good guy. My friends need me. I’m not afraid. I know I’m going to win.
He was naive, simple-minded, reckless, overconfident. Pretty accurate description for most teenage boys and young men, wouldn’t you say?
By the end of the movie he was changed. His incubated little world was shattered. Crushed. He gained a wider understanding of his own nature and who and what he was up against. He started out uninformed, arrogant, and hotheaded. He ended up informed, humbled, and reflective.
Isn’t that what we call change?