Why fixing your character's worldview isn't enough
Under your protagonist's rule for how to live sits a low opinion of themselves, and an ending that fixes only the rule lands early.
How to write the lie your character believes
Most protagonists start a story believing something about themselves or the world that isn't quite true. StoryDNA calls it The Lie. It's rarely foolish. It was learned somewhere real, it pays off often enough to keep, and your reader should half agree with it.
The Truth your protagonist ends up with isn't simply the opposite of The Lie. It keeps what was accurate in the old belief and changes the rule they drew from it. Getting that right is what makes an ending feel earned instead of convenient.
Every insight on this topic
Why your character keeps believing the lie
Your protagonist keeps their false belief because it is paying them something real, and the payout should be good enough that someone in the story admires it.
When your character's best quality looks like a danger
The Lie makes your protagonist's best quality look like a danger, so the change doesn't add a strength, it points the one they already had somewhere new.