know how

A prince, therefore, need not necessarily have all the good qualities I mentioned above, but he should certainly appear to have them. I would even go so far as to say that if he has these qualities and always behaves accordingly he will find them harmful; if he only appears to have them they will render him service. He should appear to be compassionate, faithful to his word, kind, guileless, and devout. And indeed he should be so. But his disposition should be such that, if he needs to be the opposite, he knows how. You must realize this: that a prince, and especially a new prince, cannot observe all those things which give men a reputation for virtue, because in order to maintain his state he is often forced to act in defiance of good faith, of charity, of kindness, of religion. And so he should have a flexible disposition, varying as fortune and circumstances dictate. As I said above, he should not deviate from what is good, if that is possible, but he should know how to do evil, if that is necessary.

The Prince, 57-58, Bull trans. (Penguin edition)