在观察性研究中，我们常常不得不依赖于无法直接检验的假设。
"In observational studies, we often have to rely on assumptions that are not directly testable."
生存还是毁灭。这其实不是一个问题。
知道什么都不是；想象才是一切。
The only true rebellion left is to refuse to participate in the madness of the world.
The real tragedy of the poor is that they can afford nothing but self-denial.
The world is not a wish-granting factory.