This view, this dichotomy, is popular, insidious, infuriating to me as a sufferer, and very overgeneralized as far as I can tell. I guarantee you I have suffered very 'real' depression, even been diagnosed several times if you're into that, and it just so happens that I have always been able to articulate the causes. There may be people who are not able to articulate causes at a given time, for whatever reason - but even that does not mean causes aren't there.

The way I see it is this. Life as a biological organism is a two-way interaction between your biological systems, and the putative 'outside world'. And most of what you experience as your life occurs within your brain. There is lots of feedback between your brain and the outside world, notably between your brain and the brains of others. And there is lots of feedback within your own brain, with itself. This is all true for every person, whether or not you happen to have had a run-in with the first-world, western mental health system, and received a 'diagnosis' based on someone's observation of a small part of your process that is deemed dysfunctional.

What we call depression is extremely common, but we don't like it and we wish we didn't have to experience it, so we call it an illness. But it is a very common reaction to certain types of adversity: abuse, failures, disappointments, dissolution of important relationships. Such patterns are well-known even to clinicians. The view of depression as just a 'disease' that afflicts the brain for no reason... I can't imagine where this originated. I've experienced deep depression, numerous times, and I've known people who did as well. I could tell you all the reasons. Maybe they make happy people uncomfortable. I know that when I've been happy, it has been tempting to believe that I earned it, chose it, made it for myself - something self-empowering.

The reasons for depression usually boil down to prolonged alienation and frustration. Being in a place in life that is maladaptive, and not being able to find a way out in a short amount of time. Not being able to find a job, not being able to make friends or find love, or being in a relationship that is very unhappy and not being able to get out. Being in some life situation that can't be willed out of, like having a felony record, or an incurable disease. Not having completed enough education. Having low self-esteem or perceiving oneself to be a failure, for subjective but still real reasons like being ugly, overweight, or socially awkward.

I feel like one of the causes of the persistent misunderstanding of this condition is that most people seem to want to believe happy people are in control of their happiness (whether that means being in control of their external conditions, or control of their attitude), and also want to excuse depressed people from having to be in control of their depression. This is partly sensible, and perhaps rightly motivated, because happiness is characterized by feeling in sufficient control of ones state of being, and depression is a state of prolonged lack of control. But this does not in any way suggest that the depression was random. Look behind that defeated, disconnected state of mind, turn back the clock, and you will find events that led the person into that horrible state.