Why can some old people save lives through "Xianjia"?

Personally, I think it is a lie. First of all, the diseases he can see are because some diseases can be seen from the appearance, and the patient will tell him what is uncomfortable, so he knows that some diseases can't be seen because they are beyond his knowledge. If it is true, as you said, he will see a doctor. Maybe he read a lot of medical books during his illness. As for seeing what others can't see, I don't know if it's true or not, because I discussed it with a whole dormitory when I was studying. Several students said they had seen it. As for whether it is true or not, I can only judge for myself. Personally, I am an atheist.