"In the beginning was Keynesian economics, which was ad hoc in the sense that on some important issues it relied on observed stylized facts rather than trying to deduce everything from first principles. Notably, it just assumed that nominal wages are sticky, because they evidently are. [...] In the 1960s a number of economists started trying to provide “microfoundations”, deriving wage and price stickiness from some kind of maximizing behavior. This early work had a big payoff: the Friedman/Phelps prediction that sustained inflation would get “built in”, and that the historical tradeoff between inflation and unemployment would vanish."