A very hungry fox saw some bunches of grapes hanging from an arbor. He tried and tried to reach them, but couldn't. Going away, he said to himself, "Oh, they were sour, anyway."
Moral: People who can't get something they were after decide that they don't really want it.
This fable is from Aesop's "The Fox and the Grapes". In my experience, however, people pretend they really didn't want it.