Copernican principle (N. Copernicus)
The idea, recommended by Copernicus, that the Sun, not the Earth, is at the middle of the Universe. Now we know that neither idea is accurate (the Sun is not even situated at the middle of our Galaxy, much less the Universe), but it locate into effect a long chain of demotions of Earth's and our place in the Universe, to where it is currently: On an unimpressive planet orbiting a mediocre star into a corner of a typical galaxy, lost in the Universe.