Asimov imagined the system in thorough detail. He peopled Eternity with maintenance personnel, who keep physical facilities operating, and administrators. The emphasis of the novel, however, is upon a third group, those Eternals, as they are called, who actually operate upon Reality: Observers, who gather data about the various Times; Sociologists, who calculate the effects of change on society; Life-Plotters, who calculate the effects of change on individuals; Computers, who analyze the individual acts that will produce the desired changes; and Technicians, who effect the changes in Reality. The ideal is the Minimum Necessary Change (MNC) for the Maximum Desired Response (MDR). The Technicians are the scapegoats of Eternity. Reality-changing results in guilt feelings among the Eternals, and they displace this onto the Technicians who actually accomplish the changes.