@Aedes,
Am I reading this right?
An individual being depressed is the result of internal influences only, and has nothing to do with environment, has absolutely no external influences?
To save myself the effort of typing out a long and sad scenario, I'll just ask a question: have you seen the movie
Reign Over Me? You know, Adam Sandler's family is killed in the 9-11 attacks and he falls into deep depression, is saved by an old friend who gets him treatment for depression?