The old wizard lifted his head, his face now solemn, and calmer. "Listen, Harry," said Dumbledore, "hear me well; for all who wield power must learn this in time. Some things in this world are, indeed, truly simple. If you pick up a stone and drop it again, the earth will be no heavier for it, the stars will not move from their paths. I say this, Harry, so that you know I am not pretending to be wise, when I tell you that even as some things are simple, others are complex. There are greater wizardries which leave marks upon the world, and marks upon those who wield them, as a simple Charm would not. Those wizardries demand hesitation, consideration of consequence, a moment to weigh the meaning of their marks. And yet the most intricate magics known to me are simpler than the simplest soul. People, Harry, people are always marked, by what they do and by what is done to them. Do you, then, understand how to say, 'Here is the line between hero and villain!' is not enough to say that what you did was right?"
"Headmaster," Harry said evenly, "this is not a decision I made at random. No, I don't know what exact effect this will have on every single one of the bullies present. But if I always waited for perfect information before I acted, I would never do anything. When it comes to the future psychological development of, say, Peregrine Derrick, beating up eight first-year girls probably wouldn't have been good for him. And it wasn't enough to just stop them quietly and quickly, since then they would just try again later; they had to see that there was a protective power worth fearing." Harry's voice stayed level. "But of course, since I am a good guy, I didn't want to permanently injure them or even cause them any pain; and yet the penalty had to be enough to weigh on the minds of anyone thinking about trying it again. So, after weighing the expected outcomes as best I could with my boundedly rational intellect, I thought it would be wisest to strip the bullies naked and glue them to the ceiling."