A famous art collector is walking through the city when he notices a mangy cat lapping milk from a saucer in the doorway of a store. He does a double take.
He knows the saucer is extremely old and valuable. He walks casually into the store and offers to buy the cat for two dollars.
The store owner replies, "I'm sorry, but the cat isn't for sale."
The collector says, "Please, I need a hungry cat to catch mice. I'll pay you twenty dollars for it." The owner says, "Sold," and hands over the cat.
The collector continues, "Hey, for the twenty bucks, could you throw in that old saucer? The cat's used to it, and it'll save me from buying a dish."
To which the owner replies, "Sorry, buddy, but that's my lucky saucer. So far this week, I've sold sixty-eight cats."