"Severus, I have not been able to keep a single Defense professor for longer than a year since I refused the position to Tom Riddle thirty years ago. Not one," said Albus pointedly. "Yes, I do honestly believe that there is magic at work here." At first he'd thought it a simple hazard of wartime; the sort of people who could teach Defense classes were often also the sort of people who tended to get into fights with Death Eaters, trying to defend other people. Then he'd thought it a coincidence, when it kept happening, too regularly to be statistically likely. But when his sixteenth Defense teacher in sixteen years, otherwise completely competent, had somehow managed to burn himself to death, he had given up and admitted there must be some sort of outside intervention at work. (And people were starting to be wary, around then; Professor Winchester had not been the first former Auror to take the post, but he had probably been the last.)