Some of them are also just badly written, like The Scarlet Letter - the impression that stuck with me was it took way too long to get to the point, so much so that the second half of the book contained needed context for the first half to have any meaning at all.

And I was one of the few who got it when we read it. I don't think anyone I knew realized the movie Easy A shared any themes with that book, but it was just so much better done they understood the relevant themes from it.