知彼知己，百战不殆
zhī​bǐ​zhī​jǐ​bǎi​zhàn​bù​dài

know yourself and your enemy

知彼知己，百战不殆 知彼知己，百戰不殆 zhī​bǐ​zhī​jǐ​bǎi​zhàn​bù​dài
know yourself and your enemy
know the enemy and know yourself, and you can fight a hundred battles without danger; used to express that understanding both your own situation and that of your opponent ensures success