The proverb "知己知彼，百战不殆" (zhī jǐ zhī bǐ, bǎi zhàn bù dài), meaning "Know yourself and know your enemy, and you will never be defeated in a hundred battles," is from Sun Tzu's ancient Chinese military treatise, "The Art of War" (孫子兵法), believed to have been written during the Eastern Zhou period, around the 6th century BC.Qing Palace Collection Picture Book. Beijing: Palace Museum Press.

Sun Tzu's work emphasizes the importance of thorough preparation and understanding in warfare. According to "The Art of War," comprehending one's own strengths and weaknesses, as well as those of the adversary, is essential for achieving victory with minimal risk.

Its wisdom reflects Sun Tzu's overall philosophy on strategy and warfare. Sun Tzu's teachings were highly regarded and studied by military leaders throughout Chinese history and have influenced military strategies worldwide.

The proverb remains relevant beyond the realm of warfare and is often applied in various contexts, such as business, politics, and personal relationships, emphasizing the importance of self-awareness and understanding the environment or adversaries one faces.