mathematics and ux design
Just like mathematics, UX design is a discipline with very few principles and many manifestations of those same principles over and over again. But as human beings we often mistakenly focus on manifestations and forget the underlying structures. Appearances can be fooling.
Notice that the tendency to mistake unity for multiplicity is another fundamental UX principle. (For instance, similar objects should be grouped together to hint at an underlying unity.)
Hence, just like mathematics, UX design is a discipline that is strong enough to take itself as its subject. One can study UX design itself from a UX point of view, just like one can study mathematics itself using mathematics.