Hermione turns out to be really really *bad* at a given subject.
Dudley Dursley turns out to have magical potential
Snape makes a succession of sexist comments in the first part of the book. Later, he gets turned into a woman in a magical accident caused by Neville Longbottom. Dumbledore chooses not to turn him back in order to teach him a lesson. (Remember, kids' books have Over Egged Morals)"
-songster in response to darthfi's question on the soon-to-be-released Order of the Phoenix