There was a poignant obstinacy in Albert Einstein's effort to come up with an unified field theory in his later years. Einstein's rejection of the quantum mechanical solution was based on his strong intuition. Whether his intuition was wrong is still an open question.
It is interesting how gravity has withstood all efforts of unification so far. Gravity is after all a force pertaining to the space-time structure. So there is an inevitable element of self-reference.
It is interesting to consider how the theory of relativity, derived from Mach's principle, fares with the notorious problem of the self-referential.