Toward a Predictive Theory of Depression
Professor of psychiatry here - I've spent the past 20 years trying to help folks with depression, and related illnesses, and trying to study these diseases at a genetic level. I suspect this will get me down-voted as I know the medical/biological perspective is often unwelcome on hn.
However: a key error people make here and elsewhere in speculating about depression (and suicide, and ADHD, and...) is either extrapolating only from their own experience, or from a vastly oversimplified psychology 101 perspective. For example: "Depressed people move more slowly, in a characteristic pattern called “psychomotor retardation”. Well, yes - except when they have agitated depression, characterized by psychomotor restlessness. Or, when they have neither of these. Likewise, oversimplifying by claiming it is a disease of dopamine, or serotonin, doesn't much help. When my car stops working, is it a disease of gasoline?
Part of the challenge of depression is its very heterogeneity. What we need is not more theorizing, it is more recognition that we need better treatments of all sorts.