Depression is a loose clustering of symptoms. That is fundamental to the medical understanding of a condition, but it is not how medical science normally defines an illness. It can be the way most of us think about it, but in modern medicine, that is only one of the very first steps. Part of a process which involves getting down to the anatomical specifics of what the illness is really all about.
With depression, and really most of psychiatric medicine, that just isn't realistic. Humanity doesn't yet understand the brain as well as specialists in this field pretend to. They seem to hope no one notices, much like shaman and witchdoctors of primitive times, who had some knowledge of what might help, but lacked a comprehensive understanding of the overall system they were trying to work with. What we do understand is really marginal at best, and may even prove to be outright wrong, someday.
We have an approximate idea of what causes emotions, but we don't understand which specific combinations of which specific neurotransmitters cause which specific emotions, and that's not even touching on how the neurophysiology of thought plays into it, how the endocrine system is involved, etc, etc. We can't honestly say why one person suffers depression and another does not. We can't even show that depression is ever an illness in itself, and not just a symptom of something else. We have no way to gauge severity. A cluster of symptoms that can look very similar in two different people, yet be caused by entirely different conditions. A disruption of neurochemistry, which we know can be disrupted in so many different ways.
This is to say, we do not really understand depression at all. It suggests a gross lack of understanding of a whole lot of the human condition, but I'm just talking about depression, for the moment. How are we supposed to promote awareness for something we just aren't all that aware of?
This 'depression' thing is something I've struggled with, in my own way, my whole life. I have experienced every symptom listed in the DSM-IV, and at any given point in the past 30 years, it's probably safe to say that I could have checked off the minimum of five symptoms necessary to qualify by those standards. I have been worse, I have been better, but I have never been able to get out from under this.
This has been my experience, since I was maybe six years old. Looking back on how it's all played out, I think there's a pretty good chance that this is related to the damage to my pituitary gland, which occurred at about that age. Most notably, this crippled my body's production of growth hormone, but it's likely to have had an entire cascade of systemic effects. Especially over time, during childhood and adolescent development. Not to even get into how it manifested in my life extrinsically, and the psychological effects that had on me.
My endocrine system has been way off, all my life, and this is likely to explain a few things, at the very least. Rather, it might explain a few things, if only we had a better understanding of what this insanely complex cocktail of biochemistry does, exactly.
This is just one obscure condition which can lead to some of the symptoms people call depression, but what I have, is not depression. I think the entire paradigm of how we view "mental illness" is way off.