Opportunity knocks, but it doesn't break the door down. Mark Twain said he was "seldom able to see an opportunity until it had ceased to be one." Francis Bacon wrote that "a wise man will make more opportunities than he finds." Albert Einstein noted that "in the middle of difficulty lies opportunity." And Rabelais reported, "I have known many who could not when they would, for they had not done it when they could." Is our understanding of opportunity...