A Law many people have a hard time swallowing. It makes sense to trust your friends, right? In situations involving power and influence, however, this is not correct. Friends can easily become enemies due to envy and greed. A friend may expect gifts from you after you have come into wealth/power and become hurt when those gifts don’t match his/her expectations. With an enemy, on the other hand, you know exactly where he/she stands. They don’t expect anything from you, which becomes pleasant astonishment when you put them in your employ instead of crushing them. Finally, with your enemies collected under you, you can keep a close eye on them.
From Robert Greene
