The implication that too many people will draw from that is that we just need to decide to make different decisions, and the disease will go away. But it won't - because depression isn't a choice.
The thing that you always need to remember about depression - and which Benjy mentions - is that depression is not something which you can reason with. Depression isn't a feeling. It's not a way of thinking, or a way of viewing the world. It's not something that you can choose not to suffer from. It's a part of how your brain works.
The thing that anyone who suffers from depression needs to know is that it's a disease, and that it's treatable. It doesn't matter if your friends are nice to you. It doesn't matter if you know that they love you. That kind of thinking - that kind of reasoning about depression - is part of the fundamental trap of depression.
Depression is a disease of the brain, and it affects your mind - it affects yourself in a terrible way. No amount of support from your friends and family, no amount of positive reinforcement can change that. Believing that emotional support can help a depressed person is part of the problem, because it's tied to the all-too-common stigma of mental illness: that you're only suffering because you're too weak or too helpless to get over it.This vibes closely with my own experience. If it had been easy to get out of, I would have. If it was a choice, I would have pulled myself out. It isn't. I can sit in a room filled with the people I love, part of an animated discussion, and then feel myself fading. Within 15-20 minutes I've gone from life of the party, loving and loved, to utterly alone while the party continues around me, unable to speak up, and terrified of the people I love. There is nothing about this that is voluntary. Friends spotting this and paying me attention helps: but not straightforwardly, and often by speeding up the crash so that the pieces can be put together again afterwards.
Depression changes how I view the world, how I perceive things. It is not me picking a worldview, and the depression coming as a consequence — the depression shows up, and I am unable to see the world other than through the tarry glasses it brings.
If you are stressed, sad, or bummed out, there are friends, family, dogs, campus counselors who can help.
If you are depressed, there are psychiatrists who can help.
And one really difficult step is to tell — from the inside — which case you are in.