An optimist looks at an oyster and expects a pearl. A pessimist looks at an oyster and expects ptomaine poisoning.
THE OPTIMIST (who has just been struck by a passing motor-car)—"Glory be! If this isn't a piece o' luck! Sure, 'tis the docther himself that's in ut."—Punch.
"What's an optimist?"
"An optimist is a person who'll go into a restaurant without a cent in his pocket and figure on paying for the meal with the pearl he hopes to find in the oyster."
"An optimist is a man who cherishes vain hopes, and a pessimist a man who nurses vain regrets."
"And what is a man who does both?"
"Oh, he's just a plain ordinary human."