Quote Originally Posted by Zarrgon View Post

And if you want the real world answer: JKR hated chemistry, so she made Snape a potion teacher....
That doesn't really sound plausible. I mean, she has as good as admitted that Hermione is something of a self-insert ... does that mean that Rowling secretly wanted to create insanely difficult to make chemicals in a girls' toilet despite hating chemistry?

(Besides, I really hate maths, but have always been able to acknowledge that except for that one guy in primary school, my maths teachers were pretty okay people)

Snape might be based on Rowling's chemistry teacher (is he, though? I read he was inspired by a teacher, but don't recall which subject), which would be the Doylist explanation, so to speak, but not the Watsonian one.

And since she planned the whole series out pretty early, I would suspect there is something more to it.