When a fool has made up his mind the market has gone by

A wise man changes his mind, a fool never

Every man is a fool in some man's opinion

Wit without discretion is a sword in the hand of a fool

To change one's mind is rather a sign of prudence than ignorance

He who knows not and knows not he knows not: he is a fool - shun him. He who knows not and knows he knows not: he is simple - teach him. He who knows and knows not he knows: he is asleep - wake him. He who knows and knows he knows: he is wise - follow him.