知己知彼,百战不殆

zhī jǐ zhī bǐ , bǎi zhàn bù dài

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])

知

zhī

to know

己

jǐ

self

知

zhī

to know

彼

bǐ

that

,

,

百

bǎi

hundred

战

zhàn

to fight

不

bù

no; not so

殆

dài

(literary) dangerous; perilous