"In observational studies, we often have to rely on assumptions that are not directly testable."
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。
抛弃世俗的琐事，身体就不会劳累；遗忘人生的烦恼，精神就不会亏损。
Every artist dips his brush in his own soul, and paints his own nature into his pictures.
如果你不冒险，你就无法成长。