草木皆兵 cǎo mù jēi bīng

东晋时代，秦王苻坚控制了北部中国。公元383年，苻坚率领步兵、骑兵90万，攻打江南的晋朝。晋军大将谢石、谢玄领兵8万前去抵抗。苻坚得知晋军兵力不足，就想以多胜少，抓住机会，迅速出击。
谁料，苻坚的先锋部队25万在寿春一带被晋军出奇击败，损失惨重，大将被杀，士兵死伤万余。秦军的锐气大挫，军心动摇，士兵惊恐万状，纷纷逃跑。此时，苻坚在寿春城上望见晋军队伍严整，士气高昂，再北望八公山，只见山上一草一木都像晋军的士兵一样。苻坚回过头对弟弟说：“这是多么强大的敌人啊！怎么能说晋军兵力不足呢？”他后悔自己过于轻敌了。
出师不利给苻坚心头蒙上了不祥的阴影，他令部队靠淝水北岸布阵，企图凭借地理优势扭转战局。这时晋军将领谢玄提出要求，要秦军稍往后退，让出一点地方，以便渡河作战。苻坚暗笑晋军将领不懂作战常识，想利用晋军忙于渡河难于作战之机，给它来个突然袭击，于是欣然接受了晋军的请求。
谁知，后退的军令一下，秦军如潮水一般溃不成军，而晋军则趁势渡河追击，把秦军杀得丢盔弃甲，尸横遍地。苻坚中箭而逃。
故事出自《晋书·苻坚·载记》。成语“草木皆兵”，形容神经过敏、疑神疑鬼的惊恐心理。

Every Bush and Tree Looks Like an Enemy

During the Eastern Jin Dynasty, Fu Jian, king of the State of Qin, controlled northern China. In the year383, Fu Jian led 900,000 infantry and cavalry troops to assault the State of Jin which was south of the Yangtze River. Xie Shi and Xie Xuan, senior generals of the Jin army, led 80,000 troops to offer resistance. Knowing that the Jin army was short of men, Fu Jian wanted to seize this opportunity of being much more numerous in armed forces to stage a quick attack.
Unexpectedly, the van of Fu Jian's army of 250,000 troops was defeated in the Shouchun area by an ingenious military move of the Jin army and suffered heavy losses. The senior general of the van of Fu Jian's army was killed, and there were heavy casualties of more than 10,000 soldiers. Fu Jian's army was dispirited and its morale was shaken. Many soldiers were in such a great panic that they waited for opportunities to run away. Standing on the city wall of the Shouchun City, Fu Jian and his brother Fu Rong saw that the ranks of the Jin army were in good order and that the morale of the Jin army was high. Turning to his brother, Fu Jian said, "What a powerful enemy this is! Why did people say that the Jin army was short of men?" He deeply regretted that he had taken the enemy too lightly.
Overshadowed by the disastrous defeat, Fu Jian ordered his troops to be deployed in battle formation on the north side of the Feishui River, in an attempt to regain the initiative by relying on the superior geographical conditions. Then Xie Shi and Xie Xuan, the senior generals of the Jin army, suggested that Fu Jian's army retreat a little bit, leaving some space, so that the Jin army could cross the river to conduct ooperations. Fu Jian thought that his chance had come, believing that the senior generals of the Jin army did not have the elementary knowledge of warfare. It was his plan to stage a sudden attack while the troops of the Jin army was busy crossing the river, and he was sure that his plan would word. So he willingly accepted the suggestion of the Jin army.
Unexpectedly, the moment the order to retreat was given, Fu Jian's troops were utterly routed and could by no means be controlled. Taking advantage of this favorable situation, the Jin army crossed the river, pursuing and attacking the enemy. The trooops of Fu Jian's army threw away everything in headlong flight, and the field was littered with the corpses of the soldiers of Fu Jian's army. Fu Rong was killed in the tangled fighting, and Fu Jian was hit by an arrow and ran away. The Jin army won a brilliant victory by defeating a big army with its limited armed forces.
This story comes from "The Life of Fu Jian" in the volume "Records" of The History of the Jin Dynasty. The set phrase "every bush and tree looks like an enemy" is subsequently used to refer to a state of extreme nervousness.