One of the basis assumptions of medical sciences is that your body is doing the best it can to stay healthy at all times. If true, this would mean that medicine could be treated as a more or less mechanical process where any shortfalls in the body’s resources are supplied by medical means.
How would one test if this were true? Well, for one thing, we could look for counter-examples. Take the placebo effect. Obviously, if your body is already healing itself as best it can, then giving the patient a fake treatment won’t make the body heal itself any faster — and yet the placebo effect is one of the most well-documented phenomena in medicine, to the point where there can be no doubt that the body can be encouraged to heal itself faster through simulated treatment.
Which raises the question, “If people have the capacity for improved healing, why doesn’t this get brought into play automatically?” As with most “why” questions, we don’t have definitive answers, because “why” questions tend to become unmanageably abstract almost from the beginning, which is why people in search of practical results tend to focus on “how” questions: “How do we get the body to heal itself with maximum effectiveness?”
Obviously, the placebo effect itself is pretty powerful, even when no one intends it to be, and that raises the question about, “If we’re getting such good results by accident, how do we do even better on purpose?”
There must be vast numbers of answers to this question. One of the better-understood methods is hypnosis, which, by the way, has always been pioneered by medical men, especially surgeons — people whose work has an objective outcome and are in a position to tell when something is working or not. When James Esdaile invented surgical hypnosis in the 19th century, he used it for anesthesia (this was before chemical anesthetics were available), and not only could he perform painless surgery, but the mortality rate of his patients was reduced by 80% or more.
What this means to me is that most of us have not yet learned how to fully express our bodies’ inbuilt healing powers,and the placebo effect, hypnosis, and no doubt other things move us in that direction. I doubt anyone has a precise handle on the “why” of it all, though it’s clear that, in human beings, the imagination has an enormous impact on our bodies, in ways far more subtle than “thinking stress-provoking thoughts can make you sick.” Your imagination can make you well, too, and make your life (and that of your doctor) a whole lot easier.