A clever man commits no minor blunders.
Johann Wolfgang von Goethe (1749-1832) 

A fool sees not the same tree that a wise man sees.
William Blake 

A great many people think they are thinking when they are merely rearranging their prejudices.
William James (1842-1910) 

A long habit of not thinking a thing wrong, gives it a superficial appearance of being right
Thomas Paine  - Common Sense

A love affair with knowledge will never end in heartbreak.
Michael Garrett Marino 

A prudent question is one half of wisdom.
Francis Bacon 

A reasoning, self-sufficing thing, An intellectual all-in-all!
William Wordsworth 

A wise man's question contains half the answer.
Solomon Ibn Gabriel 

Be wiser than other people, if you can, but do not tell them so.
Chesterfield, Lord 

Before God we are all equally wise - and equally foolish.
Albert Einstein (1879-1955)