“Wrong beliefs and wrong perceptions are contagious whether or not they are sincere, because dissidents tend to self-censor and act like believers. That is how entire societies, such as the Soviet Union, can be built on everyone’s publicly pretending to believe what many privately know to be false. After a while, in a community where people are struggling to conform with each other, it can be very hard, even in principle, to know whether people are sincere or faking, or even which is which.”