booksdirect: “Harry Potter is symmetrical.” Not just symmetrical - this is ring composition, favoured by Homer and other good writers. The 4th book is at the centre of the ring. JK Rowling knows her beans.
"If you make a Gryffindor mad and they storm out on you, they'll get a lot of satisfaction out of slamming the door behind them. But a Slytherin will leave it wide open, because they'll get the most satisfaction knowing they made you get up to close it."