Advertisements are important social and cultural documents. A representative sample often reflects a society’s concerns and values as accurately as well-executed surveys do. But how is this possible? How could images designed by people who don’t know, or haven’t talked to, us — and who are completely self-interested to boot – possibly reflect our innermost thoughts and feelings? Figuring out how exercises in persuasion by self-interested advertisers somehow manage to create reliable indicators of public sentiment has puzzled social scientists for a long time. Fortunately, it looks like the new social media may provide a key to solving that puzzle.