To one who has faith, no explanation is necessary. To one without faith, no explanation is possible.

有一个人从天堂来到人间旅游，他所使用的是有效三十天的减价票，他试图要把他的回程票卖掉。

I think that the thing that makes mathematics worthwhile is the fact that it has this incredible structure that you can explore and discover.

"The great secret that all old people share is that you really haven't changed in seventy or eighty years. Your body changes, but you don't change at all. And that, of course, causes great confusion."