Its because when you are in pain you become angry at the people closest to you for not feeling the same pain. They can not exactly feel what you are going through. And will not because you do not share the same body and soul. In absolute reality there is nothing that they can do. Being sick is a personal struggle that one has to endure alone.
However, emotional support from the peolpe closest to you is crucial to keep the spirit alive and hopeful to live.