Robert Greene's 48 Laws of Power | #2 Never Put Too Much Trust in Friends; Learn How to Use Enemies

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.