In What Way Princes Should Keep Their Word
Machiavelli notes that a Prince is praised for keeping his word. However, he also notes that a Prince is also praised for the illusion of being reliable in keeping his word. A Prince, therefore, should only keep his word when it suits his purposes, but do his utmost to maintain the illusion that he does keep his word and that he is reliable in that regard. Therefore, a Prince should not break his word unnecessarily.