What can be shown, cannot be said.

When something is "known for certain" and we cannot doubt it, then we cannot truly speak of knowledge. An experience is something like this, it is rather like a simple reaction, an unavoidable brain state dictated by a thin causal chain, a quale (plural: qualia) if you will. Being our brain state, an essential part of what we are, we by definition cannot doubt its existence any more than we can doubt our own existence. This causal chain is what allows us and in fact forces us to be conscious and experience things, but knowledge is something more complicated.

Being unique to our particular brain states and history, it should not be a big surprise that qualia can never be communicated to others. We are all individuals and live unique lives, and this forbids anyone from truly knowing what it is to be some other individual. We can only communicate our experiences to others by assuming a degree of similarity, but you can never truly tell a blind person what it is like to see and you shouldn't expect to. After all, the causal chain leading to the experience of vision cannot be the same for the blind person as it is for the one seeing. Simply telling the physical facts does not reproduce this causal chain and therefore cannot lead to the same brain states.

So experience is an integral brain state to the existence of our consciousness, but existence of that state does not represent the nature of reality or fundamental truth underlying all of existence in any obvious way besides perhaps simply by existing. Qualia alone tells you nothing about the underlying reality. Like an apple falling from the tree, it has no particular meaning before meaning is assigned to it by a consciousness for example by using complicated correlations and words like apple, fall, tree and such that point to some interpretation, model, history, reoccurring experience and most of the time the ability to share these experiences to certain degree with other similar creatures of our kind.

Experience cannot be said to be primary or secondary representation of truth without interpreting the experience, and immediately when an interpretation is made, a claim is made. Something is said using some kind of language and the claim becomes subject to doubt. By building beliefs which are consistent with each other, i.e. increasing coherence, we are building knowledge.

All knowledge is uncertain, if it isn't uncertain, it isn't knowledge - only a reaction. We can never be sure of what the fundamental nature of the universe is simply based on our experience, but this does not prevent us from playing the game by building coherence. This has undeniable utility and allows us to experience a life much more diverse than that of a mere reacting puppet, even if we fundamentally still are only some kind of puppets of the "second degree", without true free will, but at least we're no longer simple puppets of the "first degree".

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It is suggested that quantum entanglement emerges from the holographic principle stating that all of the information of a region (bulk bits) can be described by the bits on its boundary surface. There are redundancy and information loss in the bulk bits that lead to the nonlocal correlation among the bulk bits. Quantum field theory overestimates the independent degrees of freedom in the bulk.

https://arxiv.org/pdf/1109.3542v1.pdf