Book excerpt: Black Sabbath's Master of Reality has maintained remarkable historical status over several generations; it's a touchstone for the directionless, and common coin for young men and women who've felt excluded from the broader cultural economy. John Darnielle hears it through the ears of Roger Painter, a young adult locked in a southern California adolescent psychiatric center in 1985; deprived of his Walkman and hungry for comfort, he explains Black Sabbath as one might describe air to a fish, or love to an android, hoping to convince his captors to give him back his tapes.