One of the great things about the Harry Potter series is that it is detailed enough to be a great story, but still open enough that it allows for an entire world of fan theories, sequels and other additions. Ranker has collected some of the best fan theories in one place and some of them really are mind blowing. For example, are the Dursleys cruel to Harry because he has a horcrux inside of him and Horcruxes do make people inexplicably angry and hateful? Or were Neville's spells backfiring so long because he chose to use his father's wand rather than using a wand that actually chose him?
Check out the full list of theories over at Ranker