Every parent sees it in his son or daughter: an almost complete lack of gratitude. But a good parent understands it, because she remembers when she was an adolescent and recalls her own ingratitude. It took years for her to see what her parents knew at the time, namely how lucky she was. The expression is "reality set in"; she came to see how difficult life really is and how hard she must work to give her children what they need, but her children do not see that - for the most part, at least - , and they are not able to see it. Everything comes easy to them; life is easy. They don't have the epistemic conditions needed to understand what it took their parents to get to the place where they are now. They, the parents, have those epistemic conditions; they have a wide enough experience to understand what their children simply cannot understand at this point.
Although every good parent understands this, the epistemological implications seem to be lost on them because they are not philosophers and, understandably, do not care to think about the implications; but it is lost on many philosophers as well, at least many who call themselves realists. If reality set in, what was the child knowing prior to the moment reality set in?
The child sees the world through a model, one constructed on the basis of what he knows already, but also and probably for the most part on his imagination and what he would like reality to be. There is no doubt he is subject to an availability heuristic, as he and all of us always will be. But his complete lack of awareness of that heuristic was what allowed him to believe that his imagined world was the real world. In his case, how is it possible to talk about "objective truth"? Indeed, he sees the tree or the cat outside his mind, he makes existential judgments, comes to apprehend the natures of things gradually, but the contents of his consciousness of these things are rudimentary. A novel is far more than a dictionary; the world as he sees it has a narrative quality to it, and what he sees is, for the most part, what he has constructed.
As adults, it shouldn't be too difficult to acknowledge that the world as it appears to us now is simply that, the world as it currently appears to us. There is so much more to learn, and so much that we cannot learn at this time because the necessary epistemic conditions are absent and may remain so as a result of the limited circumstances in which we find ourselves.
What is an epistemic condition? Prior knowledge in all its diversity acquired through experience, which makes possible a specific intellectual posture, along with specific interests, questions, and problems to solve. Some of that knowledge will be certain, some will be a knowledge of uncertainties, a knowledge of probabilities that we once thought were certainties, a knowledge of limits, errors, failures, etc. I cannot make sense out of specific ideas or insights unless I come into the knowledge of other things first and am disposed in a particular way. There are experiences we will never have, and thus there are epistemic conditions that will never be, and that means there will be so much that will always be outside the purview of our understanding.
Communities also grow in understanding, and this is true of the Church as well. That growth is also the result of certain epistemic conditions that have been realized, certain experiences the community has undergone in its members. As an example of this in the context of the Church, consider the distinction between a proposition and an assertion. What the bible teaches (asserts) is very different than what is in the bible (propositions). Distinguishing the one from the other, however, is no easy task; the discernment takes place over time, that is, in history. Only gradually does the Church understand what is asserted in Scripture, that is, what the "word of God" is in the midst of what is written.
The fundamentalist, however, simply places total confidence in the way he interprets what he reads, without the slightest awareness of the precarious nature of inferences as well as the role of epistemic conditions that go into establishing the epistemic model through which he currently sees the world and in light of which he interprets the Scriptures. The Catholic submits to the teaching authority of the Church, but the Church as a whole develops her understanding of herself as she moves through history. This self-understanding is the sensus fidelium (sense of the faithful); the Church understands herself in her members, and the formulated teachings of the Church are the explicit formulation and expression of the sense of the faithful.