What life events throw you into a depressive illness?

Too much, too soon. Usually the loss of an important relationship (personal, financial, occupational, body image) will do the job. However enforced helplessness, conditions which are exceptionally stressful but unavoidable will suffice. Values we place emotionally on these things are the deciding issues. What is all-important to one person may be trivial to another and thus incapable of inciting depression.