"you know what I mean" ("x is true [for a certain definition of true, other than the correct technical definition]", etc) on both sides causes humans to believe that they adequately understand the meaning trying to be communicated, which is a hallucination.

It's true that this is often not a big deal, but which times it is and which times it is not is not known (which itself is typically not known, once again because of the convention).

Talking about the phenomenon is also contrary to conventions, and typically extremely well enforced (as I imagine you noticed during the dispute with your incorrect classmates, or else you were smart enough to not push the issue).

Ah! Yes, indeed. That was a strange, even frustrating, experience — though not as annoying as the times I failed to get deeper explanations from a teacher or a line manager.

Or, when the humans running our countries forget that they are hallucinating reality and got us (which mostly doesn't include them) into a war yet again, killing thousands of innocent people.

This one single causal phenomenon underlies everything, yet we ~refuse[1] to examine it.

[1] Here I am kind of being hypocritical, in that I assume to some degree that humans have the base capability in the first place.