The big problem life insurance had was people would buy it and they'd pay for several years and eventually they would think, well we didn't die, we're losing all this money, let's just cancel the insurance.

人寿保险的一个主要问题是,人们在购买了若干年保险后会突然觉得,我们并没有死,保费白花了,我们干脆把保险取消好了

耶鲁公开课 - 金融市场课程节选

You all know that when you do dy/dx, you're not supposed to cancel that d.

你们都知道 当你算dy/dx时,你不能把d约掉

耶鲁公开课 - 基础物理课程节选