"Let us take a given individual. Since his own ends are clearly given and he acts to pursue them, surely at least his actions can be considered efficient. But no, they may not, for in order for him to act efficiently, he would have to possess perfect knowledge—perfect knowledge of the best technology, of future actions and reactions by other people, and of future natural events. But since no one can ever have perfect knowledge of the future, no one’s action can be called “efficient.” We live in a world of uncertainty. Efficiency is therefore a chimera."
Rothbard