释义：天之险在于高不可升，地之险在于山川丘陵。王公设险以保卫国家，险的功用非常大。

传记作者的任务是复活过去，而非评判它。

States are inherently aggressive and expansionist because they exist in an anarchic international system where there is no higher authority to keep them in check.

Being busy is a form of laziness—lazy thinking and indiscriminate action.

进步的关键在于坚持和挑战传统观念的意愿。