… is from page 111 of the 1976 Vol. II (“The Mirage of Social Justice”) of Hayek’s Law, Legislation, and Liberty:
Most of the knowledge on which we rely in the pursuit of our ends is the unintended by-product of others exploring the world in different directions from those we pursue ourselves because they are impelled by different aims; it would never have become available to us if only those ends were pursued which we regarded as desirable.
