What word or phrase does your mother always say?
One of Aesop's fables. A fox tries many times to pluck some grapes that dangle invitingly over his head, but he cannot reach them. As he slinks away in disgust, he says, “Those grapes are probably sour anyway.”
Note: “Sour grapes” refers to things that people decide are not worth having only after they find they cannot have them.