The characters literally combine to paint a picture: “Open Sky, Cleave Earth”. This vivid imagery directly references the myth of Pangu, who pushed the sky up and the earth down, creating the world as we know it.
The soul of `开天辟地` comes from the foundational Chinese creation myth of 盘古 (Pángǔ). The story goes that in the beginning, the universe was a chaotic, dark egg. Inside this egg slept the giant Pangu. After 18,000 years, he awoke and, with a mighty axe, cracked the egg open. The light, pure parts (yang) floated up to become the Heavens (天), and the heavy, murky parts (yin) sank to become the Earth (地). Fearing they would merge again, Pangu stood between them, pushing the sky higher and the earth lower each day. After another 18,000 years, the world was stable, and the exhausted Pangu lay down and died. His body then transformed into the world's features: his breath became the wind, his eyes the sun and moon, and his blood the rivers. This contrasts sharply with the Western/Judeo-Christian creation story in Genesis. While the Genesis God creates the world through divine speech (“Let there be light”), Pangu's creation is a physical, violent, and self-sacrificial act. He creates order from chaos through immense personal effort and ultimate sacrifice. This imbues `开天辟地` with a sense of immense struggle, monumental effort, and foundational importance. Using this term elevates an achievement to a mythical level, suggesting it didn't just happen, but was *forged* into existence.
`开天辟地` is a formal and powerful idiom. You wouldn't use it to describe trying a new restaurant. It's reserved for events of historical or revolutionary importance.