The excerpts of "Self-Contradiction" are as follows:

The people of Chu praised those who had shields and spears, saying: "My shield is so strong that nothing can trap it." He also praised his spear and said: "My spear is so powerful that it can trap anything." Or he said: "How can I use my spear to trap my shield?" He can't respond. Husband/the indestructible shield/and the infallible spear cannot/stand in the same world.

Meaning

This idiom exposes the contradiction in the thinking of Confucian scribes who "confuse law with words". It is impossible for an unbreakable shield and an indestructible spear to both exist in the world. This Chu man one-sidedly exaggerated the role of spears and shields, resulting in a situation that cannot be justified. The contradictory stories warn people to be realistic and appropriate, and not to have the philistine habit of exaggerating or boasting. The businessman boasted nonsense and contradicted himself. As a result, he made a fool of himself and broke people's trust. This dishonest attitude is not advisable.

This idiom also tells people to seek truth from facts when speaking and doing things, and to think twice before acting. Be consistent in what you say or do, lest you end up at a point where you can't explain yourself and are left speechless by others.