知己知彼

know yourself, know your enemy (idiom, from Sunzi's "The Art of War" 孫子兵法|孙子兵法[Sun1 zi3 Bing1 fa3])

to know / to be aware

to know oneself / to be intimate or close / intimate friend

self / oneself / sixth of the ten Heavenly Stems 十天干[shi2 tian1 gan1] / sixth in order / letter "F" or Roman "VI" in list "A, B, C", or "I, II, III" etc / hexa

that / those / (one) another

know yourself and know your enemy, and you will never be defeated (idiom, from Sunzi's "The Art of War" 孫子兵法|孙子兵法[Sun1 zi3 Bing1 fa3])