When men by their practice, and perhaps too by their maxims, manifestly show that the natural beauty of virtue is not like to have much effect upon them, how is it possible to move them but by representing the folly of their conduct, and how much they themselves are in the end likely to suffer by it?
 Adam Smith, The Theory of Moral Sentiments (1759). copy citation

Context

“And in the same manner, the contrary vices of intemperance, pusillanimity, injustice, and either malevolence or sordid selfishness, come to be disapproved of, not only under their proper characters, but under the additional character of the most short-sighted folly and weakness. Epicurus appears in every virtue to have attended to this species of propriety only. It is that which is most apt to occur to those who are endeavouring to persuade others to regularity of conduct. When men by their practice, and perhaps too by their maxims, manifestly show that the natural beauty of virtue is not like to have much effect upon them, how is it possible to move them but by representing the folly of their conduct, and how much they themselves are in the end likely to suffer by it? By running up all the different virtues too to this one species of propriety, Epicurus indulged a propensity, which is natural to all men, but which philosophers in particular are apt to cultivate with a peculiar fondness, as the great means of displaying their ingenuity, the propensity to account for all appearances from as few principles as possible.” source