The essence of scientific progress is to edge up this ladder from ignorance to knowledge, and it is complicated by the fact that the ladder keeps get… - George Stigler

Prices instruct us on what people desire, but prices do not tell us why those things are desired. Our desires are accepted as a datum by economists: desires are some amalgam of biological needs, the cultural values of the society in which we grow up, and our own experiments.

A modern economic system is of extraordinary complexity. Imagine a three-dimensional jigsaw puzzle, consisting of roughly 100 million parts. Some parts touch against, let us say, 1,000 other parts. (That is, each family deals at one time or another with that many employers, banks, retail stores, domestic servants, and so on.) Other parts touch—let us be conservative—50,000 other parts (firms that sell to retailers and buy from other firms and hire laborers and so on). It would be enough of a task to fit these 100 million pieces together, but the real difficulties have yet to be mentioned. The pieces change shape quite often—a family has twins; a firm does the next best thing and invents a new product. The economist has the interesting task of predicting (in the aggregate) each of these movements. Meanwhile a busy set of people—congressmen, members of regulatory bodies, central bankers, and the like—are changing the rules on who or what the jigsaw pieces will be and how they are shaped. And of course there are other jigsaw puzzles (foreign economies) of comparable complexity, and these other puzzles are connected at literally a million points with our puzzle.

The delicate and intricate pattern of competition and cooperation in the economic behavior of the hundreds of thousands of citizens of Stockholm offers a challenge to the economist that is perhaps as complex as the challenges of the physicist and the chemist.