How to ruin all the movies: read up on all the alternate theories to how the universes in those movies work.
Wow. I had heard of a couple of these theories, but the other ones just messed with my head.
I think the Harry Potter one is just freaking depressing, though. Especially given that JK Rowling came up with things like the dementors as a representation of depression.
Slap that on top of the Harry Potter theory, and there are pretty much no good feels to be found there.
Still, I like movie theories. Do you have any favourites? Let me know.