To know the enemy and know oneself; to have a thorough understanding of both sides of a conflict or situation. This idiom originates from 孙子兵法 sūn​zǐ​bīng​fǎ (The Art of War).

to emerge victorious from every fight; to come through a hundred battles unscathed. This idiom originally comes from the 孙子兵法 sūn​zǐ​bīng​fǎ and is often preceded by the phrase 知己知彼 zhī​jǐ​zhī​bǐ