More obvious observations that seem easy to follow when you're not actually depressed.

Sometimes depression is just a matter of not having enough energy. With ample energy stores, the human mind and body become intolerant of complacency and push the individual to engage in some activity, even if a full philosophical justification has not been submitted and approved. Since action leads to more action, some kind of jump start like caffeine or a stimulant drug can get the ball rolling and sideline the depression temporarily. But to sustain such momentum is another story. It's no wonder there are so many coffee and meth addicts; people want to feel "up".

But for me, the crash that comes afterward, or the ever-deteriorating state of wellbeing and sanity that accompanies constant stimulation is not worth the positive benefits. Exercise is probably the one true "high" which doesn't make you feel bad afterward. I would imagine long, intense meditation might be another. These are the less easy ways to obtaining energy and momentum, but truer and more sustainable. Exercise and meditation. The cure to everything, seemingly.