Ipse dixit

Ipse dixit, Latin for "he himself said it", is a term used to identify and describe a sort of arbitrary dogmatic statement, which the speaker expects the listener to accept as valid.

The fallacy of defending a proposition by baldly asserting that it is "just how it is" distorts the argument by opting out of it entirely: the claimant declares an issue to be intrinsic, and not changeable.