In "Catch-22" by Joseph Heller, the concept of Catch-22 is introduced, highlighting a paradoxical rule governing military service. The rule states that a soldier can be deemed insane and therefore eligible to avoid combat duty if they request it. However, the request itself indicates a rational thought process, which implies that the soldier is sane and must therefore serve, creating a no-win situation.

This absurdity reflects the broader theme of the book, where the struggle for survival and sanity in the face of war becomes a trap. The idea that seeking safety from real danger is a sign of rationality encapsulates the bleak humor and critique of bureaucracy and war, illustrating how individuals are caught in vicious cycles created by illogical regulations.