Source: Kill the Dead
“If you are to be kept right, you must possess either good friends or red-hot enemies. The one will warn you, the other will expose you.”
Plutarch, Moralia, 74C
Quoted by Plutarch
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Diogenes of Sinope 33
ancient Greek philosopher, one of the founders of the Cynic… -404–-322 BCRelated quotes

In a State House press conference. http://www.pressherald.com/2016/08/26/house-democrats-condemn-lepage-attack-on-westbrook-legislator/ (August 26, 2016)
“If you want enemies, excel your friends; but if you want friends, let your friends excel you.”
How to Win Friends and Influence People