I don't know why we live—the gift of life comes to us from I don't know what source or for what purpose; but I believe we can go on living for the reason that (always of course up to a certain point) life is the most valuable thing we know anything about and it is therefore presumptively a great mistake to surrender it while there is any yet left in the cup. In other words consciousness is an illimitable power, and though at times it may seem to be all consciousness of misery, yet in the way it propagates itself from wave to wave, so that we never cease to feel, though at moments we appear to, try to, pray to, there is something that holds one in one's place, makes it a standpoint in the universe which it is probably good not to forsake. You are right in your consciousness that we are all echoes and reverberations of the same, and you are noble when your interest and pity as to everything that surrounds you, appears to have a sustaining and harmonizing power. Only don't, I beseech you, generalize too much in these sympathies and tendernesses—remember that every life is a special problem which is not yours but another's, and content yourself with the terrible algebra of your own. Don't melt too much into the universe, but be as solid and dense and fixed as you can. We all live together, and those of us who love and know, live so most. We help each other—even unconsciously, each in our own effort, we lighten the effort of others, we contribute to the sum of success, make it possible for others to live. Sorrow comes in great waves—no one can know that better than you—but it rolls over us, and though it may almost smother us it leaves us on the spot and we know that if it is strong we are stronger, inasmuch as it passes and we remain. It wears us, uses us, but we wear it and use it in return; and it is blind, whereas we after a manner see …
Henry James, Selected letters
depression, mind