… is from pages 387-388 of the 2014 collection, The Market and Other Orders  (Bruce Caldwell, ed.), of some of F.A. Hayek’s essays on spontaneous-ordering forces; specifically, it’s from Hayek’s previously unpublished 1961 lecture at the University of Virginia “The Economic Calculus” (which is the second of four lectures that Hayek delivered in UVA’s Newcomb Hall during the Spring 1961 semester; the title of this lecture series by Hayek is “A New Look at Economic Theory”) (editor’s footnote excluded):
It seemed to me that at least a substantial part of the benefit I had derived from the study of economics, and of what I accepted as the criterion of a good economist in others, was not any knowledge of fact, or even of particular laws which economic phenomena obey, but rather a capacity of discovering and refuting certain kinds of fallacies of reasoning. I don’t think there can be any doubt that this is one of the most common and not least important tasks of the economist to correct not errors of fact but errors of reasoning.