personality factors are important for those loops - e.g. lose job, very conscientous but highly neurotic, feels depressed about not having a job, falling into depression, marriage suffers, isolation from friends, positive emotions and enthusiasm decreases, drinking problems develop, etc.
meaning that depression is not necessarily happening because something is wrong in somebody's head - it may as well be just because something went wrong in their life
however - their psychological inadequacies might be interfering with their ability to recover, or served as precursors for their issues in the first place
you're not just an individual - you're connected to other people through society, job, friends, etc. - all sorty of networks that can pull you down, or elevate you!