The statesman， who should attempt to direct private people in what manner they ought to employ their capitals， would not only load himself with a most unnecessary attention but assume an authority which could safely be trusted， not only to no single person， but to no council or senate whatever， and which would nowhere be so dangerous as in the hands of a man who had folly and presumption enough to fancy himself fit to exercise it.

工具变量的美妙之处在于它们让我们以新的视角看世界。

创新不是重新发明轮子，而是让轮子转得更顺畅、更快。

最好的学生是那些从不相信老师的学生。