The new trade theory picture of the world looks something like this: Each country has, at any given time, a set of broad resources—land, skilled labo… - Paul Krugman

Economics is harder than physics; luckily it is not quite as hard as sociology. Why is economics such a hard subject? Part of the answer has to do with complexity. The economy cannot be put in a box. [...] Another reason economics is hard is that the critical sociologist is right: it involves human beings, who do not behave in simple, mechanical ways.

A temporary evolution of ignorance, a period when our insistence on looking in certain directions leaves us unable to see what is right under our noses, may be the price of progress, an inevitable part of what happens when we try to make sense of the world's complexity.

Keynes didn’t make an all-out assault on Economic Man, but he often resorted to plausible psychological theorizing rather than careful analysis of what a rational decision-maker would do. Business decisions were driven by “animal spirits,” consumer decisions by a psychological tendency to spend some but not all of any increase in income, wage settlements by a sense of fairness, and so on.
But was it really a good idea to diminish the role of Economic Man that much? No, said Friedman, who argued in his 1953 essay “The Methodology of Positive Economics” that economic theories should be judged not by their psychological realism but by their ability to predict behavior. And Friedman’s two greatest triumphs as an economic theorist came from applying the hypothesis of rational behavior to questions other economists had thought beyond its reach.