In the lives of the saddest of us, there are bright days like this, when we feel as if we could take the great world in our arms and kiss it. Then come the gloomy hours, when the fire will neither burn on our hearths nor in our hearts; and all without and within is dismal, cold, and dark. Believe me, every heart has its secret sorrows, which the world knows not, and oftentimes we call a man cold, when he is only sad.

Henry Wadsworth Longfellow, Hyperion

In the Greek myth, Sisyphus, with great effort, rolls a large rock up a mountain. At the top, the rock, of its own inertia, rolls back down again. Doomed to roll the rock up the mountain over and over again to no avail — this is what life often feels like to those in extreme despair.