I believe that the human being is a very robust creature, both mentally and physically, and does not normally succumb to disease, to stressors or to mild bodily abuse (like drinking too much, or "burning the candle at both ends"). Millions of years of evolution — working on the principle of surival of the fittest — has made us very tough, and has given us the best of genes.
This is the precise argument put forward by evolutionary biologist
Paul W. Ewald: he says that most common diseases will not turn out to have genetic causes, and are not due to some inherent weakness in the human being. Ewald explains that any disease-causing gene that reduces survival (and reproduction) will eliminate itself over a number of generations. So chronic diseases such as diabetes, multiple sclerosis, anxiety disorders, chronic fatigue syndrome, schizophrenia, clinical depression, etc cannot be primarily genetic, according to the logic of evolutionary biology.
So if it is not genes and not inherent weakness, what causes these diseases then?
Well, once you catch a few pathogens, these are the one thing that can destroy the normal health and harmony of your body, because pathogens too have been harnessing the immense power of evolution — but in this case, for the purposes of their own survival, not yours. Their survival is your downfall. So once you start accumulating a few pathogens in your body, it becomes a battle, and this is where disease begins.
One day , the human race will wake up to the fact that it has been pathogens all along that have messed things up for us. And then, once the penny drops, and we have our "ah-ha" moment, we will finally do something about it.
But until that day, not only will pathogens will continue to win, but we will also have to put up with all these unscientific psychogenic theories put forward by Wessely school psychologists and the like.