Knowledge without sense is twofold folly

Men can acquire knowledge, but not wisdom. Some of the greatest fools ever known were learned men.

He who knows nothing, doubts nothing

It is better to conceal one's knowledge than to reveal one's ignorance

The simple inherit folly: but the prudent are crowned with knowledge.

Knowledge profits those who know how to use it. Ignorance hurts those who use it. Folly ruins those who practice it.