in the philosopher's stone when harry said "not slytherin" the sorting hat responded " not slytherin you could be great you know it is all hear in your head and slytherin can lead you to greatness, are sure ok gryffindor" why would slytherin lead him to greatness. the hat told harry ARE YOU SURE of this choice like he was going to make a mistake. book 2 he said i stand by what i said last year. what did slytherin have that other houses didn't? i need the best answers you can think not something at the top of your head. p.s. i know that students in the ceremony can make there own choices. but what about slytherin that the sorting needed harry to be in it.