悲伤是爱变成了永恒的缺失。
In the state of nature, indeed, all men are born equal, but they cannot continue in this equality. Society makes them lose it, and they recover it only by the protection of the laws.
心理学的方法必须是客观的，即使研究主观现象时也是如此。
Happiness is not something ready made. It comes from your own actions.