"How praiseworthy it is for a prince to keep his word and live by honesty and not deceit, everyone knows; nevertheless we see, by what goes on in our own times, that those princes who have accomplished great things are the ones who had cared little for keeping promises and who knew how to manipulate the minds of men with shrewdness; and in the end they won out over those who founded themselves on loyalty."
-- Niccolò Machiavelli (1469-1527), Italian philosopher and writer
The Prince (1532)
Ch. XVIII, "How a Prince Should Keep His Word"
Translated by Mark Musa.