Characters have a tendency to grow, change and evolve as they deal with the events of the story. But they don't become completely different people, there is still some aspect of their original personality that exists.
This trope is about how characters like to think that they or someone else has improved themselves, but the reality is that you don't change overnight and there will be many aspects of what makes you special that will never completely go away.
Compare It's What I Do
, I Am What I Am
. Contrast Characterization Marches On
and That Man Is Dead
- A season 8 episode of Scrubs had J.D. dealing with Denise, a bright but very insensitive intern who struggles to connect with patients. In a conversation about it she asked J.D. what he was going to do to fix her and he said he wasn't going to do anything, because it was her character flaw to deal with. He goes on to point out that despite having grown significantly in the past few years his girlfriend (Elliot) still struggles with her own neurosis, his teacher (Dr. Cox) is constantly getting in his own way and J.D. himself struggles with being too close to patients to be objective about what they need, complete with quick cuts to those exact problems.
- In The Big Bang Theory Leonard and Penny try hanging out together on a friend date, only for things to go sideways because Leonard realized since he and Penny weren't dating anymore he didn't have to conform to exactly what she wanted. After getting into a heated argument, Leonard later apologized and Penny commented that some part of her LIKED that he showed some backbone for a change (hinting that was one reason she broke up with him). He inadvertently backtracked to his needy self, but was a marked example of his character development.