I will answer with an example. There exist some interpretations of quantum mechanics. One of them is the [many-worlds interpretation][1] : > It is a philosophical position about how the mathematics used in > quantum mechanics relates to physical reality. It asserts that **the > universal wave function is objectively real**, and that ... Whether you know quantum mechanics or not, is irrelevant here, the key point is that a mathematical construct (wave function) is considered as a "real" object. This is the *epistemic fallacy* that he is referring to: because a wave function does not exist, it's a construct, it's only what we can know or understand about the "real". [1]: https://en.m.wikipedia.org/wiki/Many-worlds_interpretation