A lot of people get complacent during normal times and they assume that normal times will go on forever.

风平浪静时人们容易变的自满,他们认为这太平盛世会持续到永久

耶鲁公开课 - 金融市场课程节选

Nowadays, if you go to outer space, you can check for yourself that if you throw something out, it just goes on forever without your intervention.

现如今,如果你去了外太空,你可以向外抛个物体试试,如果你不打断它,它就会一直运动下去

耶鲁公开课 - 基础物理课程节选