in ad 383, the king of former qin (秦朝), fu jian (fú jiān 苻坚), led a huge army to attack eastern jin.
　　公元383年，秦王苻坚率领步兵、骑兵90万，攻打江南的晋朝。

   　after losing the first round of fighting, fu jian looked down from a city wall, and was terrified when he saw the formidable battle array of the eastern jin army.
　　在一轮战败后，苻坚从城墙俯视周遭，当他看到势不可破的东晋部队，他感到很害怕。

　　and then looking at the mountains around, he mistook the grass and trees for enemy soldiers.
　　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，于是更加恐慌。

　　as a result, when the nervous fu jian led his army into battle, it suffered a crushing defeat.
　　后来苻坚全军覆没，带着少数残余的队伍逃回去了。

       this idiom describes how one can defeat oneself by imaging difficulties.
　　这个成语后来形容人在极度惊恐时，疑神疑鬼的心理状态。


　　【文化链接】

　　英文中“草木皆兵”的相应说法可以用“afraid of one's own shadow”，也就是一个人连自己的影子都怕，当一个人连自己的影子都怕的时候，是不是就是疑神疑鬼，“草木皆兵”了呢~~

　　我们来一起看一个例句吧~

　　she stays at home all the time and never makes any new friends. she seems to be afraid of her own shadow.
　　她老待在家里, 从不交新朋友，感觉“草木皆兵”。