自然实验可以为经济问题提供有价值的见解。
Natural experiments can provide valuable insights into economic questions.
The thing about happiness is that you only know you had it when it's gone.
Not he who has much is rich, but he who gives much.
技术是这样一种诀窍，它安排世界，使我们不必去体验它。
人渴时，一滴水就像甘露一样甜美；人醉后，再添酒还不如不添的好。
和一个道德品质败坏的人，无法完成一桩好交易。