Natural experiments can provide valuable insights into economic questions.

译文：一个人的脾气性格不平和，无论是做事还是做学问，都不可能有上进；一个人油嘴滑舌，夸夸其谈，那么这个人的品质和心术就值得怀疑了。赏析：不论是做事还是做学问，一定要平心定气，心无二用，方能有所成就。伶牙俐齿本不是坏事，但油嘴滑舌，言过其实，这样的人就应该警惕。

The degree of slowness is directly proportional to the intensity of memory; the degree of speed is directly proportional to the intensity of forgetting.

你们会选择安逸的生活，还是选择一个奉献与冒险的人生？