“Clearly, there are only four kinds of student: brave but not smart, smart but not evil, evil but not brave, and chubby.”
“Well yes, obviously.”
“And the way to teach these students is to have a talking leather hat decide which one they are and then make them fight each other.”
In hindsight Rowling’s self-loathing and hatred of any idea of self-selected identity is obvious from the text. None of her characters choose for themselves who or what they want to be.