In 1951 Solomon Asch setup a similar experiment asking people which of these lines is the same as this one. A, B or C? Even though the answer is obvious many people answered C. How could that be? Just like at the diner, the actual subject of the test was choosing last. Before him were paid actors that gave the same wrong answer, "C, C and C". Without knowing it they influenced the subject to conform just as you conformed to decline dessert.