These characters combine literally to mean “People's determination triumphs over Heaven/Nature.” It conveys a powerful message of humanity's potential to shape its own environment and future.
Historically, this idiom is associated with the Chinese spirit of collective struggle against natural disasters, a constant theme in Chinese history (e.g., the taming of the floods by the mythological emperor Yu the Great, 大禹治水). It embodies a deep-seated belief in the power of organized, collective human labor. The phrase gained immense prominence during the Maoist era (1949-1976) as a political slogan to mobilize the population for massive state projects like the Great Leap Forward. It was used to justify monumental engineering feats, such as building dams and re-routing rivers, with the belief that sheer manpower could reshape the country and overcome any material or natural limitations. Because many of these projects had severe environmental consequences, the term can sometimes carry a negative connotation of human arrogance and a disregard for nature. This concept contrasts sharply with some Western philosophical or religious ideas like “acceptance,” “letting go and letting God,” or the Stoic concept of amor fati (love of one's fate). While Western thought often emphasizes finding peace by accepting what one cannot change, 人定胜天 is a call to action to change what seems unchangeable. It is the philosophical opposite of fatalism.
The usage of 人定胜天 today is nuanced and highly context-dependent.