Finding out the prices of a large range of commodities is itself a costly enterprise, and knowledge of this fact by price setters is itself enough to… - Kenneth Arrow

Speaking very broadly, almost any human action involves choice; the external environment delimits a range of possible actions at any given moment but does not usually reduce that range to a single alternative. The formulation of a theory of human action in some sphere as a theory of choice means its presentation as a functional relation associating with each possible range of alternatives a chosen one among them.

Certainly, there is no general principle that prevents the creation of an economic theory based on other hypotheses than that of rationality.

I don't know which way human psychology will go wrong. We have a world in which there is uncertainty. There are new technologies. And one of the problems is that we do things today with a thought to the future. Any purchase is one for the future. If you buy a refrigerator you are making a commitment to the future, so that you have food to eat for the next ten years. That's a simple theory, one of many simple theories -- theories that people agree on and that don't, in a fundamental way, change. But every once in a while there is unemployment, and wages will drop, and there will be several different interpretations.