Maybe it was a case of Great Expectations. Maybe Charles Dickens nailed that beast which causes clinical depression. Since age 11 until age 58 I was a depressive. That ended when I ended being so determined to become a card-carrying member of The Establishment Download Geezerguts. The efficiency of depression is that it's such a painful state that we are willing to actually change to exit it. Yeah, it's that bad.
The current edition of THE ECONOMIST reports that research, e.g. the JOURNAL OF PERSONALITY AND SOCIAL PSYCHOLOGY, found that there might be a link between the onset of depression and the pursuit of unattainable goals. When we surrender to the impossibility of those goals, accept a more realistic path, the depression lifts.