The Duke would not pay for the works. He says that the Castle can never be taken. That is called hubris, Giacomo, the belief that you are never wrong. Believing you are never wrong is an error that afflicts great men. I have learned that to be right you must first be wrong many times. Without making errors--and learning from them--a man cannot find the truth.
Christopher Peter Grey, Leonardo's Shadow: Or, My Astonishing Life as Leonardo Da Vinci's Servant
errors, hubris, mistakes, truth