No regulation of commerce can increase the quantity of industry in any society beyond what its capital can maintain. It can only divert a part of it into a direction into which it might not otherwise have gone; and it is by no means certain that this artificial direction is likely to be more advantageous to the society than that into which it would have gone of its own accord. Every individual is continually exerting himself to find out the most advantageous employment for whatever capital he can command. It is his own advantage, indeed, and not that of the society, which he has in his view. But the study of his own advantage naturally, or rather necessarily leads him to prefer that employment which is most advantageous to the society.

Chapter II, p. 486. - The Wealth of Nations (1776) - Book IV