Pay or contest
Ross, Greene and House (1977) gave this story, in dollars and miles per hour, to 80 Stanford students. Before saying what they would do, each estimated what share of their peers would pay and what share would go to court; here, you chose first and estimated after. Then 46% said they would pay, and 54% that they would contest. Those who chose to pay had estimated, on average, that 71.8% would pay and 28.2% contest; those who chose to contest, that 51.7% would pay and 48.3% contest. Each group rated its own choice as more common than the other group did: the authors called this the false consensus effect.
Ross, L., Greene, D., & House, P. (1977). The “false consensus effect”: An egocentric bias in social perception and attribution processes. Journal of Experimental Social Psychology, 13(3), 279-301.