Delusions have been around since people have been around, “but that delusions often bear a complicated relationship to the cultural context in which they occur. During the Cold War, for instance, there was an uptick in people believing they were under surveillance by the C.I.A. or F.B.I.” The rise of the “Truman Show” delusion has coincided with the advent of reality television and other media in which people actually are recorded and broadcast all the time. “We’re raising our children with the notion that you, too, can be famous tomorrow.”