… is from page 6 of A.C. Pigou ‘s June 1954 Diogenes article, “Some Aspects of the Welfare State ,” as quoted by Bruce Caldwell in his editor’s note that appears on page 226 of F.A. Hayek’s June 1962 lecture, “The Economy, Science and Politics” (available on-line here ) as that essay is reprinted in the 2014 collection of some of Hayek’s essays on spontaneous-ordering forces, The Market and Other Orders  (Bruce Caldwell, ed.) (brackets are from Caldwell):
It must be confessed, however, that we seldom know enough to decide in what fields and to what extent the State, on account of [the gaps between private and social costs] could usefully interfere with individual freedom of choice. Moreover, even though economists were able to provide a perfect blueprint for beneficial State action, politicians are not philosopher kings and a blueprint might quickly yield place on their desks to the propaganda of competing pressure groups.
Doing economics or policy analysis under the dual assumptions that state operatives typically possess, or have ready access to, adequate information to intervene ‘correctly’ and that these operatives reliably behave as unbiased and apolitical social engineers is not to do science; it is instead to be in the grips of an ages-old dogma. It is to practice a superstition. It is to be blind to the reality of human nature and to the empirical record of state actions throughout time. It is to act on faith – faith that these two assumptions hold in reality when, in fact, experience and reason tell us that they do not hold in reality.