Every one understands how praiseworthy it is in a Prince to keep faith, and to live uprightly and not craftily. Nevertheless, we see from what has taken place in our own days that Princes who have set little store by their word, but have known how to overreach men by their cunning, have accomplished great things, and in the end got the better of those who trusted to honest dealing.
Be it known, then, that there are two ways of contending, one in accordance with the laws, the other by force; the first of which is proper to men, the second to beasts. But since the first method is often ineffectual, it becomes necessary to resort to the second. A Prince should, therefore, understand how to use well both the man and the beast. And this lesson has been covertly taught by the ancient writers, who relate how Achilles and many others of these old Princes were given over to be brought up and trained by Chiron the Centaur; since the only meaning of their having for instructor one who was half man and half beast is, that it is necessary for a Prince to know how to use both natures, and that the one without the other has no stability.
Nicolo Machiavelli, The Prince, Chapter XVIII