[I]n most social situations, if not in all, there is an element of rationality. Admittedly, human beings hardly ever act quite rationally (i.e. as they would if they could make optimal use of all available information for the attainment of whatever ends they may have), but they act, none the less, more or less rationally; and this makes it possible to construct comparatively simple models of their actions and inter-actions, and to use these models as approximations.
Karl Popper, The Poverty of Historicism, 1957, p. 130