Edward de Bono Quote

A person who knows all the answers, has an opinion on everything, has a certainty backed up by rational argument, has very little possibility of further progress. Such a person is unlikely to walk away from a discussion with anything more than a reaffirmation of how right he or she has been all along.

I Am Right, You are Wrong: From this to the New Renaissance : from Rock Logic to Water Logic (ed. Penguin Group USA, 1991)