“The only teacher that's worth anything to you is your enemy.”

“An enemy, Ender Wiggin," whispered the old man. "I am your enemy, the first one you've ever had who was smarter than you. There is no teacher but the enemy. No one but the enemy will tell you what the enemy is going to do. No one but the enemy will ever teach you how to destroy and conquer. Only the enemy shows you where you are weak. Only the enemy tells you where he is strong. And the rules of the game are what you can do to him and what you can stop him from doing to you. I am your enemy from now on. From now on I am your teacher.”

“I am your enemy, the first one you've ever had who was smarter than you. There is no teacher but the enemy. No one but the enemy will tell you what the enemy is going to do. No one but the enemy will ever teach you how to destroy and conquer. Only the enemy shows you where you are weak. Only the enemy tells you where he is strong. And the only rules of the game are what you can do to him and what you can stop him from doing to you. I am your enemy from now on. From now on I am your teacher. I will devise the strategy of your army, and you will learn to be quick and discover what tricks the enemy has for you. Remember, boy. From now on the enemy is more clever than you. From now on the enemy is stronger than you. From now on you are always about to lose.”

“Personal affection is a luxury you can have only after all your enemies are eliminated. Until then, everyone you love is a hostage, sapping your courage and corrupting your judgment.”

“Home is anywhere that you know all your friends and all your enemies.”

“We know everything we knew that was worth knowing, that's a crucial distinction.”

“The criminal misuse of time was pointing out the mistakes. Catching them―noticing them―that was essential. If you did not in your own mind distinguish between useful and erroneous information, then you were not learning at all, you were merely replacing ignorance with false belief, which was no improvement. The part of the man's statement that was true, however, was about the uselessness of speaking up. If I know that the teacher is wrong, and say nothing, then I remain the only one who knows, and that gives me an advantage over those who believe the teacher.”