Tyrion: Ah...rapers. They were given a choice, no doubt. Castration or the Wall. Most choose the knife. Not impressed by your new brothers? Lovely thing about the Watch. You discard your old family and get a whole new one.
Jon: Why do you read so much?
Tyrion: Look at me and tell me what you see.
Jon: Is this a trick?
Tyrion: What you see is a dwarf. If I had been born a peasant, they might have left me out in the woods to die. Alas, I was born a Lannister of Casterly Rock. Things are expected of me. My father was the Hand of the King for 20 years.
Jon: Until your brother killed that King.
Tyrion: Yes, until my brother killed him. Life is full of these little ironies. My sister married the new King, and my repulsive nephew will be king after him. I must do my part for the honor of my house, wouldn't you agree? But how? Well, my brother has a sword, and I have my mind. And a mind needs books like a sword needs a whetstone. That's why I read so much, Jon Snow.