During the Chu-Han contention, Han general Han Xin led tens of thousands of troops to attack the Zhao kingdom, which was then allied with Xiang Yu, the King of Chu.
King Zhao Xie and his general Chen Yu held Jingxing Pass (north of modern Jingxing, Hebei) with about 200,000 troops—several times the Han army's size. Han Xin knew a conventional battle would mean certain defeat, so he employed the tactic of "placing troops in a death ground to make them fight for survival." He deliberately stationed a force by the Mianman River near Jingxing, arranging them with their backs to the water.
When the Zhao soldiers saw Han Xin's unconventional formation, they couldn't help but laugh, and even his own officers struggled to understand. As the battle began, Han Xin feigned defeat and retreated to the position by the Mianman River, then turned around to fight again.
When the two armies clashed again, Han Xin's troops fought like an entirely different force—every soldier charged with such ferocity that each man seemed worth ten, routing the Zhao army completely and sending them fleeing in utter disarray.
After the battle, generals presented enemy heads and captives to report their achievements to Han Xin. At the victory feast, as they freely discussed the campaign, they remained puzzled by his tactics—especially the river-back formation. One general asked, "General, deploying troops with our backs to the river goes against military convention. How did you know it would succeed?" Han Xin smiled and replied, "This is recorded in *The Art of War*: 'Place your men in a desperate position, and they will fight to survive.' With no retreat, every soldier fought as if their life depended on it—and that is why we won."
A general, unable to hold back, asked Han Xin, "General, I have a question for you. The Art of War says to choose a position with mountains to the right and rear, and water to the left and front. But why did you order us to fight with our backs to the river, going against the rules of warfare?"
Han Xin smiled slightly and replied, "This formation method of mine can also be found in military texts; it's just that you didn't think of it."
Upon hearing this, the generals eagerly pressed for more, each asking in turn.
Han Xin added, "Doesn't the art of war say, 'Place troops in a death ground and they will fight to live; put them in a hopeless position and they will survive'? Only by stationing soldiers where death threatens will each man fight for his own life and battle desperately."
After hearing Han Xin's explanation, the generals suddenly saw the light and were utterly awestruck by his strategic brilliance.
Later, people used the idiom "Each Fights for Himself" to mean everyone can fight independently.
Source: *Records of the Grand Historian*, "Biography of the Marquis of Huaiyin"
Meaning of the Idiom: Later, the Chinese idiom "人自为战" came to describe everyone can fight independently.