Einstein was skeptical about quantum mechanics to his death. He didn't refute it or describe it as bad physics; the mathematics were meticulous and experimentally proven accurate. But he felt they were incomplete.

Quantum mechanics was very good at what it was describing, but it was limited. Its results were so bizarre and counter-intuitive that something must have been missing in its description of reality. On the other hand, Einstein must have realized that leveling such a description of quantum mechanics opened up his theories of relativity to the same accusation.

If he couldn't refute quantum mechanics, then his theories of relativity were also incomplete and did not truly or fully describe reality. And that, I suppose, is why he pursued a theory of everything, merging quantum mechanics and relativity to his death.

My thinking and my bias is that even if a theory of everything is reached, perhaps the ultimate triumph of scientific process and theory, I still look at science with Einstein's own suspicious eye. It's very good at what it's describing, but it is successful because it limits itself.

Quantum mechanics works fine in the atomic realm, and as long as it limits itself to the realm of the very small, it's primo. Same with relativity; as long as it limits itself to the realm of the very large, the science is irrefutable.

But to me, I wonder if this explaining the realm of the very small and the realm of the very large, even if explained in a unified theory, explains the whole of reality. It might still do what it does very well because it limits itself. Physics describes the physical world, but it assumes the physical world is all there is.

And there's plenty of stuff in the basic existential human experience to suggest that assuming the physical world is all there is is fundamentally delusional, incomplete and arguably unsatisfying.