The only purpose for which power can be rightfully exercised over any member of a civilized community， against his will， is to prevent harm to others.

Every ton of coal we extract carries equal weight in responsibility.

我步入丛林，因为我希望生活有意义。我希望活得深刻，吸取生命中所有的精华，把非生命的一切都击溃。

工具变量的美妙之处在于它们让我们以新的视角看世界。