Here’s my theory. The Harry Potter trio are actually representations of the other houses. Hermione is Ravenclaw. Ron is Hufflepuff. Harry is Slytheryn. They’re all in Gryffindor because they asked. In fact, everyone in that house could have been in another house if they hadn’t asked to be in Gryffindor. You have be ask to be in Gryffindor because their most defining feature is bravery and anyone can choose to be brave.