变老最好的事情是你不会失去你曾经经历过的所有年龄。
The best thing about getting older is that you don't lose all the other ages you've been.
The most important thing in mathematics is to understand the concepts, not just to memorize the formulas.
"The only limit to our realization of tomorrow is our doubts of today."
真相很少纯粹，也绝不简单。