Because that's how personalities work. No one can teach you to have a dominant attitude or strong mind.
What?
Yes, yes you can.
You think people are a bunch of anime characters that dont go through changes in their lives or something?
Someone can teach you how to discipline yourself, how to be "dominant", etc.
Difficulty varies from person to person.
I can assure you I'm not the same person I was 10 years ago. Or that version of "me" was the same as the one 10 years before that.
CoC is luck.
You either are born with it, something you have no control over, or you will never have it.
There's no "personality" thing involved here.