[yomly]

> it would be the instant death of one personality and their replacement by a different one. And that feels very uncomfortable to people.

That's a salient observation, but it's a definitely a curious aversion and possibly linked to a similar underlying thought pattern that "growth mindset" vs "fixed mindset" tries to capture:

Notions like "I can become more confident in everything I do" and "I can learn to be better with people" terrified a friend as some kind of type of desire to deceive others with some inauthentic persona that was disingenuous because you had changed your personality

[AndrewDucker]

I guess it depends on how core you view certain parts of your personality as being.

If "you" is "an introvert who isn't good with people", then "learning to be good with people" must be some kind of faking it. Rather than a change in view/approach which actually makes you like people and not be afraid of them.