A chronic lack of pleasure, of any enjoyable, rewarding or stimulating experiences, produces a slow, gradual, day-by-day erosion of man's emotional vitality, which he may ignore or repress, but which is recorded by the relentless computer of his subconscious mechanism that registers an ebbing flow, then a trickle, then a few last drops of fuel--until the day when his inner motor stops and he wonders desperately why he has no desire to go on, unable to find any definable cause of his hopeless, chronic sense of exhaustion.