Law 2
Be wary of friends – they will betray you more quickly, for they are easily aroused to envy. They also becomes 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. –Robert Greene, The 48 Laws of Power (review)