The phrase "The sky is falling!" is a popular idiom derived from the fable of Chicken Little, also known as Henny Penny.

Meaning: It expresses a sense of panic or hysteria, often based on little to no evidence. It suggests that someone is overreacting to a situation, believing that disaster is imminent when there's no real cause for alarm.

Origin: The story of Chicken Little involves a chicken who is struck on the head by a falling acorn. The chicken then jumps to the conclusion that the sky is falling and runs around warning everyone, causing widespread panic.

Usage: The phrase is used to dismiss someone's exaggerated fears or warnings.