… is from page 312 of the late University of Washington economist Paul Heyne ‘s deeply wise 1995 article in Agenda titled “Teaching Introductory Economics ,” as it’s reprinted in the 2008 collection of Heyne’s writings, “ Are Economists Basically Immoral?” and Other Essays on Economics, Ethics, and Religion  (Geoffrey Brennan and A.M.C. Waterman, eds.) (footnotes deleted):
We are doing blackboard economics whenever we demonstrate, usually with the aid of a blackboard graph, the non-optimal character of a situation and the Pareto superiority of some alternative arrangement, all without paying any attention to what arrangements real people can actually make and the costs of doing so. Standing at the blackboard seems to confer upon many economists, at least in their own imaginations, such divine attributes as omniscience, impartial benevolence, and omnipotence. They suppose that they are whispering in the ear of a benevolent and all-powerful despot, to employ James Buchanan’s telling complaint about this way of doing economics.
DBx: The fact that today most such analyses are done, not on blackboards, but on whiteboards or in PowerPoint slides does nothing to deflate the economists’ conceit that Heyne here describes.