The Guilty Blood

"Guilt is powerful," Sirius said. "It has teeth and claws, and once it sinks them into you, it doesn't let go. You'll spend the rest of your life wondering what you could have done differently. I know guilt, Harry, and you don't want to do this to yourself." Harry has a tendency to blame himself for things that aren't his fault. Luckily, Sirius is there to set him straight.