This allusion comes from Writings of Hanfeizi·Hindrance·The First Volume：
故事出自《韩非子·难一》，大意是说:
A man of the state of Chu had a spear and a shield for sale.
有一个卖矛和盾的楚国人。
He was loud in praises of his shield.
他大声的夸奖他的盾：
“ My shield is so strong that nothing can pierce it through.”
“我的盾是最坚固的，没有东西能刺透它。”
He also sang praises of his spear.
接着，他又赞美他的矛，说:
“My spear is so strong that it can pierce through anything. ”
“我的矛是最锐利的，它能刺透任何东西。”
“What would happen”，he was asked, “if your spear is used to pierce your shield?”
有人问他：“那如果用你的矛去刺你的盾，会怎么样呢？”
He was unable to give an answer.
卖矛和盾的人回答不出来了。
It is impossible for the strongest shield to coexist with a spear that finds nothing impenetrable.
世界上不可能同时存在最坚固的盾和最锐利的矛。
Now this allusion is used to refer to the case of being selfcontradictory and inconsistent.
后人就用“自相矛盾”一词来比喻言论或行动前后自相抵触，互不相容。
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