Another is the loss of a love or loss of a job or of identity, and that's grief. In grieving you can feel depressed or sad. The fifth one is having a faulty childhood resulting in poor self-esteem or no sense of self. You are emotionally down because of your dislike for yourself. This is a psychodynamic depression.
Most clinicians only know about the last one, the psychodynamic depression.
Psychiatrists have more training in the clinical depression and usually prescribe anti-depressants. Because of Vietnam there is now more understanding of post-traumatic stress depression. But in the depression related to grief, the training is almost non-existent. Yes, but they may also miss the other kinds. There tends to be a bias in the observer.