Cause of depression. Stress. The longer you are depressed, the harder it is to beat. The more you are stressed with no reprieve, the higher the chances that you will get depressed. Factor in a person't tolerance to stress and knowledge on how to deal with it, and it is almost impossible to predict who will get clinically depressed. Then factor in those with anxiety already, and the poor brain can suffer some permanent damage.
Your brain + stress = effect.
This old analogy of mine: Bang your knee, and stop. You might get a bruise. Continuously bang your knee nonstop and you will eventually get permanent damage. Your brain can suffer a permanent chemical imbalance. It is chemicals that cause the minor case of blues or full blown depression.
We are also seeing that "what doesn't kill you, makes you stronger" is not the case here. The more damage that is done, the less tolerance you have to stress.
http://www.medicinenet.com/script/main/art.asp?articlekey=35249
Yes, I know that having had depression doesn't make me an expert, but I've had to learn all I can.
I just wish I knew how to manage stress instead of making things worse. Then maybe I could have been spared years of wallowing in hell.
I did eventually learn, and do accept that depression can be managed as a disease.
"Years of research has told us that people do become sensitized to stress and that this sensitization actually alters physical patterns in the brain," says Seymour Levine, Ph.D., of the University of Delaware. "That means that once sensitized, the body just does not respond to stress the same way in the future. We may produce too many excitatory chemicals or too few calming ones; either way we are responding inappropriately."
...Unfortunately, when stresses become routine, the constant biochemical pounding takes its toll on the body; the system starts to wear out at an accelerated rate.
I will testify to this.
One way it can be managed, if the brain cannot mend on its own with stress management and psychotherapy alone, is with drugs. That again is an argument that depression is a disease, right? The drugs can act as a bandaid to allow the brain time to heal, or it may have to be a permanent solution in severest cases. The drugs are rather useless without behavorial change if that is what is causing some of the depression - by putting unnecessary stress on the brain.
I do recommend reading all the pages of the article to get the full explanation. I've read books on it, so a few pages of reading will help if one hasn't much experience with it.
Stress management is a personal discovery. One thing that works for one person may not help another at all. Live and learn.