"This fellow is wise enough to play the fool; And to do that well craves a kind of wit: He must observe their mood on whom he jests, The quality of persons, and the time, And, like the haggard, check at every feather That comes before his eye. This is a practise As full of labour as a wise man's art For folly that he wisely shows is fit; But wise men, folly-fall'n, quite taint their wit."

Source: William Shakespeare (1998). “Twelfth Night, Or, What You Will”, p.156, Oxford University Press, USA