If you didn't read the books:

 

You wouldn’t know who Peeves was.
You wouldn’t know how the Weasley Twins made WWW coming from a poor family.
You wouldn’t know about Dumbledore and Grindelwald.
You wouldn’t know much about the Marauders.
You wouldn’t know about Voldemort’s past.
You wouldn’t know the TRUE meaning of “Always.”
You wouldn’t know much about Neville’s past.
You wouldn’t know much about Remus and Nymphadora.
You wouldn’t know about Teddy.
You wouldn’t know or understand the struggle of Draco Malfoy.
You wouldn’t know what really went on at the Quidditch World Cup.
You wouldn’t know much about Snape’s past.
You wouldn’t know or understand the true depth of Harry’s relation with Sirius.
You wouldn’t know about Winky.
You wouldn’t know about Dobby and his sacrifices.
You wouldn’t know much about Horcrux’s.
You wouldn’t know about how the final Horcrux happened and how it was destroyed.
You wouldn’t know anything about Luna’s room.
You wouldn’t know about Dean in Shell Cottage.
You wouldn’t know that Harry repaired his own wand and returned the Elder Wand to its original place.
You wouldn’t know about the true importance of the Deathly Hallows.
You wouldn’t know about S.P.E.W.
You wouldn’t know about Harry, Ron and Hermione’s O.W.L grades.
You wouldn’t know that Dudley said to Harry: “I don’t think you’re a waste of space.”
You wouldn’t know who Snuffles is.
You wouldn’t know that Weasleys came to pick Harry from Dursleys for Quidditch World Cup.
You wouldn’t know how Alastor ‘Mad-Eye’ Moody died.
You wouldn’t know that the curse that chopped George’s ear off was actually Snape trying to cut another Death Eater’s wand.
You wouldn’t know the creatures Lupin introduced in third year, like the Grindylow.
You wouldn’t know what happened to Buckbeak.
You wouldn’t know that Draco and Tonks are cousins.
You wouldn’t know how to get to the kitchen.
You wouldn’t know that Stan Shumpike became a Death Eater.
You wouldn’t know about Sirius’ mum’s portrait.
You wouldn’t know how Remus became a werewolf.
You wouldn’t know about Victorie & Teddy.
You wouldn’t know Tonks’ parents.
You wouldn’t know Fred’s complete death.
You wouldn’t know Neville’s parents at St. Mungo’s.
You wouldn’t know about the apparating sessions.
You wouldn’t know how Firenze took place of Divination teacher for a while.
You wouldn’t know much about anything.