明于知己，暗于知彼

语出毛泽东《中国革命战争的战略问题》。意谓对自己一方比较了解，而对敌人那一方情况则不甚了解。这种人“是不能解决战争规律的学习和使用问题的”。彼：他人，指敌人。

明于知己，暗于知彼míng yú zhī jǐ , àn yú zhī bǐ

have a good knowledge of oneself but a poor knowledge of others; understand oneself but not others
❍ 有一种人，～，又有一种人，明于知彼，暗于知己，他们都是不能解决战争规律的学习和使用的问题的。(《毛泽东选集》166)Some people are good at knowing themselves and poor at knowing their enemy,and some are the other way round; neither can solve the problem of learning and applying the laws of war.