Both quantum mechanics and the theory of relativity give rise to extremely complicated math and processes that are difficult for even the most advanced physicists to understand.

It is my feeling that the underlying rules that make a universe must be very simple because if it were HARD to make a universe, the universe would certainly not exist and we (as a result) would not be here right now.

This is where the “Occam’s Razor” principle comes into play where the simplest solution is the preferred solution.