A Beatles song offers perhaps the most concise explanation of why nostalgia works so well as a marketing tactic: "Yesterday, all my troubles seemed so far away. Now they look as though they're here to stay. Oh, I believe in yesterday." When times are tough, when things get bad, it's human nature to gaze back fondly at eras that seem less tumultuous. The impulse may not be the most logical response to real-time, real-world problems -- another lyric from "Yesterday," "Now I need a place to hide away," suggests it could be futile -- but it's understandable.