Poka-yoke is a Japanese term that means “mistake-proofing” or “error-proofing”. Simply put, poka-yokes are mechanisms that make errors visible or, in their most advanced form, impossible to do. The world is full of poka-yokes, some designed on purpose, some not.
You can find one example in the picture. A broken subway turnstile with a sticker that a) tells everybody that the mechanism is broken, and therefore, not ready to use and b) prevents any customer from putting the subway ticket in the slot (what will have unexpected consequences)