知己知彼，百战不殆

zhī jǐ zhī bǐ , bǎi zhàn bù dàizhijizhibi,baizhanbudai

1. 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])

Study it in Yanamino