… is from page 347 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, this quotation is from Hayek’s January 1970 lecture at the University of Salzburg, “The Errors of Constructivism “:
Science can help us to a better theoretical understanding of the interconnections [that form a complex economy]. But science cannot significantly help us to ascertain all the widely dispersed and rapidly fluctuating particular circumstances of time and place which determine the order of a great complex society.
The delusion that advancing theoretical knowledge places us everywhere increasingly in a position to reduce complex inter-connections to ascertainable particular facts often leads to new scientific errors.
Astute readers will see the relevance of this quotation to Russ’s most-recent post .