  Every Bush and Tree Looks like an Enemy 草木皆兵 

  In AD 383, the king of Former Qin, Fu Jian, led a huge army to attack Eastern Jin. 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. And then looking at the mountain around, he mistook the grass and trees for enemy soldiers. As a result, when the nervous Fu Jian led his army into battle, it suffered a crushing defeat. 
  公元383年，前秦国王苻坚带了80万大军攻打东晋。在淝水一带，被晋朝大将谢玄的前锋部队打得大败。苻坚登上寿阳城，看见晋军阵容严整，心里害怕起来。再远望八公山上长着许多草和树木，也以为是东晋的士兵，更加惊恐万分。后来苻坚终于全军覆没，带着少数残余的队伍逃了回去。

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