The man who employs either his labour or his stock in a grater variety of ways than his situation renders necessary, can never hurt his neighbour by underselling him. He may hurt himself, and he generally does so. Jack of all trades will never be rich, says the proverb. But the law ought always to trust people with the care of their own interest, as in their local situations they must generally be able to judge better of it than the legislator can do.

Chapter V, Digression, p. 572. - The Wealth of Nations (1776) - Book IV