Professor Lupin: Why do you look so miserable, Harry?
Harry: None of it made any difference. Pettigrew escaped.
Professor Lupin: Didn't make any difference? Harry, it made all the difference in the world! You helped discover the truth. You saved an innocent man from a terrible fate. It made a great deal of difference.
Harry drops in to find Professor Lupin packing to leave Hogwarts, having resigned his post.