Never put too much trust in friends, learn how to use enemies. 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.
— ROBERT GREENE, THE 48 LAWS OF POWER