Unsuspectedly from the bottom of every fountain of pleasure, as the old poet said, something bitter rises up: a touch of nausea, a falling dead of the delight, a whiff of melancholy, things that sound a knell, for fugitive as they may be, they bring a feeling of coming from a deeper region and often have an appalling convincingness. The buzz of life ceases at their touch as a piano-string stops sounding when the damper falls upon it.

Of course the music can commence again; — and again and again — at intervals. But with this the healthy-minded consciousness is left with an irremediable sense of precariousness. It is a bell with a crack; it draws its breath on sufferance and by an accident.

Even if we suppose a man so packed with healthy-mindedness as never to have experienced in his own person any of these sobering intervals, still, if he is a reflecting being, he must generalize and class his own lot with that of others; and, doing so, he must see that his escape is just a lucky chance and no essential difference. He might just as well have been born to an entirely different fortune. And then indeed the hollow security! What kind of a frame of things is it of which the best you can say is, “Thank God, it has let me off clear this time!” Is not its blessedness a fragile fiction? Is not your joy in it a very vulgar glee, not much unlike the snicker of any rogue at his success?

— William James, The Varieties of Religious Experience