During the Eastern Jin Dynasty, Fu Jian, ruler of the State of Qin, controlled northern China. In 383 AD, he led a massive army of 900,000 infantry and cavalry to attack the State of Jin, located south of the Yangtze River. The Jin forces, led by generals Xie Shi and Xie Xuan, mustered only 80,000 troops for defense. Confident in his overwhelming numerical advantage, Fu Jian sought a swift victory.
Unexpectedly, the 250,000-strong vanguard of Fu Jian's army was decisively defeated at Shouchun by a clever Jin military maneuver, suffering over 10,000 casualties, including the death of its commanding general. This disastrous loss shattered the morale of Fu Jian's troops, with many soldiers becoming panic-stricken and looking for chances to flee. Observing the Jin army's orderly ranks and high spirits from the city wall, Fu Jian remarked to his brother, Fu Rong, "What a formidable enemy! Why did people claim the Jin army was weak?" He deeply regretted underestimating his foe.
Reeling from the defeat, Fu Jian redeployed his forces along the north bank of the Feishui River, hoping to regain the initiative using the favorable terrain. The Jin generals then proposed that Fu Jian's army retreat slightly to allow the Jin troops space to cross the river and engage. Fu Jian saw this as a golden opportunity, believing the Jin commanders lacked basic military knowledge. He planned to launch a sudden attack while the Jin army was mid-crossing and readily agreed.
However, the moment the retreat order was given, Fu Jian's army fell into utter chaos and could not be controlled. Seizing this advantage, the Jin army crossed the river and launched a fierce assault. Fu Jian's troops fled in disarray, abandoning their equipment, and the battlefield was strewn with their corpses. Fu Rong was killed in the chaotic fighting, and Fu Jian, wounded by an arrow, escaped. The Jin army achieved a brilliant victory against vastly superior numbers.
This story originates from "The Life of Fu Jian" in the Records section of The History of the Jin Dynasty. The idiom "every bush and tree looks like an enemy" is derived from this event and describes a state of extreme paranoia and nervousness.