A man from the state of Lu presented two intricate knots to King Song Yuangong.
The king issued a proclamation, seeking wise individuals to untie them, but no one succeeded.
Later, a student of Er Shou managed to untie one knot but could not undo the other. He then declared, "This knot is impossible to untie." The king sent messengers to verify this claim with the man from Lu.
The man from Lu replied, "He is correct. This knot cannot be untied. I was the one who tied it, knowing it was impossible to solve. He, who did not tie it himself, can discern its nature. He is surely wiser than I am."