自然实验是理解现实世界中因果关系的强大工具。
Natural experiments are a powerful tool for understanding causal relationships in the real world.
这世界上聪明的人,努力的人太多了,要得到你想要的东西,最可靠的办法,是让自己配得上它。
"The only thing worse than being blind is having sight but no vision."