In the reign of Charles II. a physician to the court was walking with the
king in the gallery of Windsor Castle, when they saw a man repairing a
clock fixed there. The physician knowing the king's relish for a joke,
accosted the man with, "My good friend, you are continually doctoring
that clock, and yet it never goes well. Now if I were to treat my
patients in such a way, I should lose all my credit. What can the reason
be that you mistake so egregiously?" The man dryly replied, "The reason
why you and I, Sir, are not upon a par is plain enough--the sun discovers
all my blunders, but the earth covers yours."