Folie a Deux: In FRPG's, participants collectively construct a fantasy world. The world may have the collective creation of an entire culture and world, including language, religion, governments, social customs, and all of these can bring gamers into a condition similar to "shared madness", or a delusional system set in paranoid beliefs not accepted by those outside of their "real" social world. In a gaming sense, gamers share a "fantasy" they help build. Fantasy gamers see this fantasy as systemic, logical, and resalistic, and can thus make assumptions about how the game functions. The gamer can disassocite the fantasy or delusional world and their real world.
Source: Fine, G. A. (1983). Shared fantasy. Chicago: University of Chicago Press, p. 12