The idiom zi xiang mao dun - "spear against shield from one hand" - describes words or actions that contradict each other, arguing against yourself.
Story: a man of Chu sells spears and shields. He praises the shield: "My shield is unbreakable - nothing can pierce it!" Then the spear: "My spear is unstoppable - nothing can withstand it!"
Someone asks: "Then what happens when your spear meets your shield?" The seller is struck dumb - a shield that stops everything and a spear that pierces everything cannot both be true.
Meaning: speech and deeds must stay consistent; the word maodun (contradiction) comes from this tale (spear = attack, shield = defence).
Examples: "You supported it this morning and oppose it this afternoon - is that not zi xiang mao dun?" / "Policy cannot contradict itself, or people will not know what to follow."
Opposites: zi yuan qi shuo (make your account hold together) and shouwei huying (head and tail consistent).
The tale: in the Warring States, a man of Chu sold weapons. First he praised his shield: "My shield is impenetrable; no spear can pierce it."
Then he praised his spear: "My spear is the sharpest; it pierces every shield."
Someone asked: "What if you pierce your shield with your spear?" He could not answer - his words contradicted each other.
From Han Feizi. "Zì xiāng máo dùn" became one of China most used idioms.
It means: saying or doing things inconsistently, conflicting with oneself.
Today it criticises: people whose words contradict themselves, systems whose rules conflict, behaviour that says one thing and does another.
It reminds us: speak consistently, act logically - one who cannot make sense of himself is hard to trust.
For learners it is useful: check your logic in expression; do not contradict yourself.
Remember: spear and shield cannot both be "best in the world". Think before you speak, and you will not slap yourself.
The tale reminds us to speak and act logically. A claim that cannot survive questioning is not a good claim.
Chinese praise people as "kào pǔ" - reliable: promises kept, words consistent. That is the everyday version of "no self-contradiction".
As a learner, be a "reliable" speaker: think before speaking, speak clearly before acting.
The tale also teaches a life truth: "zhī xíng hé yī" - knowing and doing as one. Saying one thing and doing another is everyday self-contradiction. Chinese value "words matching deeds" most. For learners, this is lesson one of expression: think the logic through before speaking; review after writing. When you can "round out your words", your Chinese has matured a big step.
Finally, a test: if someone first says "I love travelling" then "I hate going out", what do you say? - Self-contradiction. Correct, you have truly learned it.
One-sentence summary: think three seconds before speaking, reflect three times after acting. The consistent are trusted everywhere.
