You couldn't changed history. But you could get it right to start with. Do something differently the FIRST time around. This whole business with seeking Slytherin's secrets... seemed an awful lot like the sort of thing where, years later, you would look back and say, 'And THAT was where it all started to go wrong.' And he would wish desperately for the ability to fall back through time and make a different choice. Wish granted. Now what?

You are personally responsible for becoming more ethical than the society you grew up in.

There is no justice in the laws of nature, no term for fairness in the equations of motion. The Universe is neither evil, nor good, it simply does not care. The stars don't care, or the Sun, or the sky. But they don't have to! WE care! There IS light in the world, and it is US!

Do not flinch from experiences that might destroy your beliefs. The thought you cannot think controls you more than thoughts you speak aloud. Submit yourself to ordeals and test yourself in fire. Relinquish the emotion which rests upon a mistaken belief, and seek to feel fully that emotion which fits the facts.

Maybe you just can't protect people from certain specialized types of folly with any sane amount of regulation, and the correct response is to give up on the high social costs of inadequately protecting people from themselves under certain circumstances.

I only want power so I can get books.

When you are older, you will learn that the first and foremost thing which any ordinary person does is nothing.