每个人都有不为世人所知的秘密悲伤；我们常常称一个人冷漠，其实他只是悲伤。
"Every man has his secret sorrows which the world knows not; and often times we call a man cold when he is only sad."
The concept of NP-completeness has provided a powerful tool for understanding the complexity of computational problems.
写作是探索人类心灵复杂性的一种方式。