I want to know the answer to the following question:
Where did  Feynman find success before moving to quantum gravity
All the background I'm provided with is that "The computational device that Feynman discovered then for gravity, "ghosts", which are "particles" in the interior of his diagrams that have the "wrong" connection between spin and statistics, have proved invaluable in explaining the quantum particle behavior of the Yang–Mills theories, for example, QCD and the electro-weak theory.". Is that enough to answer the question?
Answer: no