The only way to learn mathematics is to do mathematics.
学习数学的唯一方法就是做数学。
在空闲的时候不做准备，危急的时候却临时抱佛脚。国家发生战乱时，才想到有名的将领；家庭贫困时才希望能有个贤惠的妻子。
The knowledge that you have emerged wiser and stronger from setbacks means that you are, ever after, secure in your ability to survive. You will never truly know yourself, or the strength of your relationships, until both have been tested by adversity. Such knowledge is a true gift, for all that it is painfully won, and it has been worth more than any qualification I ever earned.