定义就是限制。
说某事就是执行一项行动，而执行行动就是用言辞来实现某事。
On the path of science, there are no smooth roads to take; only those who are not afraid of hard work and climb the steep mountain paths have the hope of reaching the glorious summit.
环境对不同观察者会显得不同，这取决于他们准备看到什么。