The Copernican principle is the idea that Earth does not sit at the center of universe or is otherwise special in any way. When Nicolaus Copernicus first stated it in the 16th century, it led to an entirely new way to think about our planet.
Since then, scientists have applied the principle more broadly to suggest that humans have no special privileged view of the universe. We are just ordinary observers sitting on an ordinary planet in an ordinary part of an ordinary galaxy.
This form of thinking has had profound consequences. It led Copernicus to the idea that Earth orbits the sun and Einstein to his general theory of relativity. And it regularly guides the thinking of physicists, astronomers and cosmologists about the nature of the universe.