The mediocrity principle simply states that you aren’t special. The universe does not revolve around you; this planet isn’t privileged in any unique way; your country is not the perfect product of divine destiny; your existence isn’t the product of directed, intentional fate; and that tuna sandwich you had for lunch was not plotting to give you indigestion. Most of what happens in the world is just a consequence of natural, universal laws—laws that apply everywhere and to everything, with no special exemptions or amplifications for your benefit—given variety by the input of chance. Everything that you as a human being consider cosmically important is an accident. The rules of inheritance and the nature of biology meant that when your parents had a baby, it was anatomically human and mostly fully functional physiologically, but the unique combination of traits that make you male or female, tall or short, brown-eyed or blue-eyed, were the result of a chance shuffle of genetic attributes during meiosis, a few random mutations, and the luck of the draw in the grand sperm race at fertilization.
Source: The Mediocrity Principle