容易得到的东西，是靠不住的；轻易许下的诺言，不值得信赖。
Thinking is the hardest work there is, which is probably the reason why so few engage in it.
The first erroneous assumption is that quality means goodness, or luxury, or shininess, or weight. Quality means conformance to requirements.
Nothing is impossible, the word itself says I'm possible’!
数学的本质不仅在于解决问题，还在于提出正确的问题。