No matter what he does， every person on earth plays a central role in the history of the world. And normally he doesn't know it.
无论他做什么，地球上的每个人在世界历史中都扮演着核心角色。而通常他并不知道这一点。
"The success of machine learning depends on the ability to balance the trade-off between bias and variance in the models we build."
"In computer science, we are always trying to find the balance between expressiveness and tractability."