Related:

• He who knows others is wise. He who knows himself is enlightened. -- Lao Tsu
• He who knows not and knows that he knows not is ignorant.
  Teach him. He who knows not and knows not that he knows not is a fool....
• A wise man knows everything, but a shrewd man knows everyone.
• A wise man knows everything; a shrewd one, everybody.
• The person who quite clearly knows nothing but thinks that he knows absolutely everything has a very distinct orientation toward a political career.
• The fool doth think he is wise, but the wise man knows himself to be a fool.
  -- William Shakespeare (1564-1616), As You Like It -- Act v, Sc. 1...
• The truly proud man knows neither superiors or inferiors.
  The first he does not admit of -- the last he does not concern himself about. -- William Hazli...
• He that knows nothing, doubts nothing.
• A really busy person never knows how much he weighs. -- Edgar Watson Howe