自然实验是理解现实世界中因果关系的强大工具。
"I guess that’s just part of loving people: You have to give things up. Sometimes you even have to give them up."
"Traveling is a brutality. It forces you to trust strangers and to lose sight of all that familiar comfort of home and friends. You are constantly off balance. Nothing is yours except the essential things: air, sleep, dreams, the sea, the sky - all things tending towards the eternal or what we imagine of it."
自由不是一种状态，而是一种态度。
"The act of writing is an act of courage."