百战不殆/ 百戰不殆 bǎizhànbùdài (also bǎizhànbúdài) to win every battle
to emerge victorious from every fight; to come through a hundred battles unscathed. This idiom originally comes from the 孙子兵法 sūnzǐbīngfǎ and is often preceded by the phrase 知己知彼 zhījǐzhībǐ