6. The Defence Against The Dark Arts Position Is Cursed
It's something of a running gag at the beginning of the Harry Potter series: every year there's a new Defence Against The Dark Arts teacher, as it seems like every year some baffling (or often quite horrific) fate befalls the staff member who rises to fill the position. Take Professor Quirrell, for example, who had a half-formed Lord Voldermort strapped to the back of his head. Or Lockhart, who loses his memory due to a backfiring memory charm. Not only that, but it's a well-known fact that Snape has been pining over the position for years. He's clearly qualified, so why does he never get to take it? Snape is repeatedly denied this position by Dumbledore. As we later learn, Snape is feeding information to Dumbledore about Voldemort and his plans by pretending to be loyal to the Dark Lord. That's a fairly important job to be responsible for, and practically invaluable. One theory states that the reason for all this is that Voldemort has cursed the position. After returning to Hogwarts as Tom Riddle, Riddle requests that he be allowed to teach the Dark Arts. Once he's rejected by Dumbledore (who can see his heart as it truly is) Riddle is enraged, and casts a curse meaning that no-one can assume the position for more than a year. Throughout the books its strongly implied that something is legitimately wrong with the Defence Against The Dark Arts teaching position, so this theory is more than likely right.
