One is led to conclude that economics as a scientific discipline is still somewhat hanging in the air. - Tjalling Koopmans

One can in particular interpret the proposition as a statement conditions under which the simplicity of incentive structure and the economies of information handling characteristic of a competitive market organization can be secured without loss of efficiency of allocation... The price system carries to each producer, resource holder, or consumer a summary of information about the production possibilities, resource availabilities and preferences of all other decision makers. Under the conditions postulated, this summary is all that is needed to keep all decision makers reconciled with a Pareto optimal state once it has been established.

According to a frequently cited definition, economics is the study of “best use of scarce resources.” The definition is incomplete. “Second best” use of resources, and outright wasteful uses, have equal claim to attention. They are the other side of the coin.

Decisions and plans made by others... [can be judged to be] quantitatively at least as important as the primary uncertainty arising from random acts of nature and unpredictable changes in consumers' preferences.