An utter impossibility; something that will never happen.
想要不劳而获，那简直是马角乌头，绝无可能
To wish for gains without any effort is an utter impossibility, like horses growing horns and crows turning white.
Era:
Ancient
Frequency:
Story:
In the late Warring States period, the states of Qin and Yan outwardly maintained friendly relations, exchanging royal princes as hostages. Prince Dan of Yan was a hostage in Qin, and King Ying Zheng of Qin treated him with great disrespect and contempt.
Prince Dan requested permission from the Qin King to return to Yan. The King replied that he could only return when horses grew horns and crows turned white.
Prince Dan then escaped back to Yan and dispatched Jing Ke to assassinate the Qin King.
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