After a friend asked me how she could tell what exactly triggers a depressive episode and if an inferiority complex could contribute to depression. I remember telling her inferiority complex could contribute to the onset of an episode if, events capable of causing depression had accumulated in the course of life. I suggested; one way was to take stock of recent life events that may contribute to triggering an episode.
I recently came across a literature and would like to share what I learnt with my readers.

The onset of depression is a cumulative effect, having an uncharacteristic behaviour that is influenced by hidden variables. In the face of a major depression, one tends to look back for the roots of it; wondering whether it was always there or whether it came on suddenly as food poisoning. Having a breakdown when you have experienced trauma or when your life is a mess is clearly understandable. But having an episode when everything seems fine and you are finally in a good place is confusing. Depression does not always stem from recent life events. Factors leading to a breakdown gather over the years, usually a lifetime.

Severely threatening life events usually trigger initial breakdowns, the second episode, somewhat less; and for subsequent episodes, life events may play no part at all. It then becomes random and endogenous, dissociated from life events. (Look up The stress of depression on some factors that contribute to the dissociation of episode from event triggers).

Physical trauma is among the primary triggers for psychiatric trauma. We all encounter periods of physical and psychological trauma and chances are high, that people with a significant vulnerability will relapse in the face of a problem. So do not consider intolerance for extreme pain, whether physical or psychological as a weakness of character.