Relativism
“Man is the measure of all things, of the things which are, that they are, and of the things which are not, that they are not… Each thing appears to me, so it is for me, and as it appears to you, so it is for you—you and I each being a man.” – Protagoras, as quoted by Plato in his Theaetetus. This is the first known writing on relativism, a worldview that is common in culture today.