A doctor, no matter how good he is, cannot cure a fatal illness. No power is unlimited. No matter how skillful a doctor is and how advanced the medical facilities are, it is not possible to cure all diseases. There are always some diseases that cannot be cured and some lives that cannot be saved. This is very unfortunate yet inevitable. People should face this reality rationally and calmly. The expression is also used to remind people of force majeure and the limitations of human beings.