The greatest sweetener of human life is Friendship. To raise this to the highest pitch of enjoyment, is a secret which but few discover.

The most important thing is to keep the most important thing the most important thing.

I’m a very positive thinker, and I think that is what helps me the most in difficult moments.

The work is always changing.

自然实验是理解现实世界中因果关系的强大工具。