We all hold some assumptions to be true and they lie too deep to be proved; one could call them framing beliefs. Like a frame, those fundamental beliefs are not part of the picture (i.e. our daily experiences, our world-view, our norms...), but they give it its shape, its outline, its orientation.
Every individual, and every culture, has framing beliefs that determine their fundamental stance towards the world. Those beliefs shape the way we see things, how we talk about them and the way we respond. Usually we are not conscious of them, precisely because they are frames, not part of the picture. It takes some effort to unearth our own assumptions. The vast majority of people save themselves this trouble, even among the educated classes.