Never seem wiser or more learned than the company you are with. Treat your knowledge like a watch and keep it hidden. Do not pull it out to count the hours, but give the time when you are asked.
—Philip Stanhope, 4th Earl of Chesterfield (by Allan Ramsay; Public Domain)

Few things betray a person faster than their own hubris. Arrogance quickly reveals itself to the audience, but remains strangely hidden from the speaker.
—Mike Hazell