Once a disease has entered the body all parts which are healthy must fight it: not one alone but all. Because a disease might mean their common death. Nature knows this and Nature attacks the disease with whatever help she can muster.
We run into some pretty tough arguments sometimes but the idea is that at the end of the day my wife and I realize that we'll always be holding each other's hand. This is a lifelong relationship and after 12 years she hasn't gotten rid of me yet.