The Gordian Knot

Origin
The Gordian Knot was created when the Phrygians, without a king, followed the oracle’s prophecy and declared Gordias, the foretold man sent by the gods, king. Gordias tied his ox-cart with an impossible knot when Alexander the Great arrived and tried to untie it by slicing it with his sword. It is often used as a metaphor for an intractable problem (disentangling an "impossible" knot) solved easily by cheating or thinking outside the box ("cutting the Gordian knot").

Effects
The knot cannot be untied by any conventional methods. If the user tries to do so, they will be killed.