In a study, researchers arranged for a man to violate the law by crossing the street against red light right into traffic. In half the instances, he was dressed in a business suit and tie. In the other half, he wore a work shirt and trousers. The study showed that three times as many pedestrians were swept along behind the man into traffic, against the light, and against the law, when he wore a suit.
Social proof, coined by Robert Cialdini, is a powerful psychological phenomenon of assuming the actions of others in an attempt to reflect correct behavior for a given situation.
Primary origin: Robert Cialdini