I've been aware of the idea since my late teens or early twenties or so, but I've really come to appreciate in the last couple of years to what degree the information your senses tell you is subjective to the point of approaching total fiction.

For an example, the other day while I was preoccupied brushing my teeth, I felt something between two toes. Immediately I assumed it must be an ant crawling on me, which freaked me out. When I was done brushing my teeth, I found it was instead very definitely just a small rock.

Chronic pain can also work this way sometimes. When you experience a distressing injury and don't understand the real severity of it, this can create a feedback loop of fear that trains you to over-interpret signals as pain, which remains with you for a very long time after the original cause of the pain has been treated. This of course is very frustrating and difficult to treat, because the pain is still very much real despite being a misinterpretation, and doctors are kinda shit about this.

I think on some level most Art also works like this. Something is constructed for the primary purpose of being perceived and interacted with in some way (even if only passively). You quickly learn (or maybe even just instinctually understand) that such things exist in a broad category, and then gradually build up a mythology about the category itself that elevates all things within it (one might call this "pretension").

Naturally, you can play with this (which in turn is More Art), and doing so tends to make some people very, very mad, because you're fucking with the comfortable illusion they built up which they aren't even aware of. Readymades are a great example of this.