"Mathematics is not about numbers, equations, computations, or algorithms: it is about understanding."
数学不是关于数字、方程、计算或算法：它是关于理解的。
Free education is abundant, all over the Internet. It's the desire to learn that's scarce.
真相总是一种侮辱或玩笑，谎言通常乏味。
If you're not failing occasionally, you're not pushing hard enough.