Be wary of friends—they will betray you more quickly, for they are easily aroused to envy. They also become spoiled and tyrannical. But hire a former enemy and he will be more loyal than a friend, because he has more to prove. In fact, you have more to fear from friends than from enemies. If you have no enemies, find a way to make them.
The 48 Laws Of Power (ed. Profile Books, 2010) - ISBN: 9781847651341