《管子·参患》
如果等到攻城围邑以后，才知道守城者易子而食，烧骨为炊的顽强抵抗，那只好一进攻就自己宣告拔寨而退了。
攻城围邑，主人易子而食之，析骸而爨之，则攻之自拔者也。
If we wait until after the siege of the city to find out that the defenders are cannibalizing their children and burning their bones to cook, we will have no choice but to declare our own withdrawal as soon as we attack.