Scientific tragedy of late

Einstein. He tried hard to unify all fundamental forces in a framework like his

General Relativity. While GR ranks among the greatest achievements of physics, UFT never worked out.
According to

CF von Weizsäcker, Einstein's UFT was far from explaining
sharply separated types of elementary particles, while

Heisenberg's attempts on UFT came a little closer.

It's an unsolved problem to fit

gravitation and

quantum physics into one mathematical framework.