彼を知り己を知れば百戰殆からず

Japanese

For pronunciation and definitions of 彼を知り己を知れば百戰殆からず – see the following entry.
かれおのれれば百戦殆ひゃくせんあやうからず
[phrase] (literal) know the other side and yourself, a hundred battles will not be perilous
[phrase] (figurative) it is important to understand the strength and weakness of your side and the opposing side, in order to mitigate the risk of failure
(This term, 彼を知り己を知れば百戰殆からず, is the kyūjitai of the above term.)