But as you get older and you have a lot of spare time, you think about what you are doing, which is something I have the luxury of doing right now, and I realized this is more tricky.

但随着你们年龄的增长,有更多空闲时间之后,你就会思考你做的事情,我现在就有很多闲暇思考这些问题,我意识到这东西其实很精妙

耶鲁公开课 - 基础物理课程节选