He who knows not and knows not that he knows not, is a fool — shun him!
He who knows not and knows that he knows not, is unlearned — teach him!
He who knows and knows not that he knows, is asleep — awaken him!
He who knows and knows that he knows, is enlightened — follow him!
Arab proverb quoted by Lady Isabel Burton (1831–1896) in The Life of Captain Sir Richard F. Burton
(Source: apprenticeship-patterns.labs.oreilly.com)