The author was sort of like me. When I entered my Ph.D., I had a dream of finding something really big. But I was disappointed to find that those low hanging fruits of big questions had been answered. Those left were impossible to answer with current technology. People were just guessing the answers by some hints, rather than evidences. I decided to leave to do a very ordinary job after getting my Ph.D.. I do not regret it. What I have learned is if you really like a subject, you should be fine with solving those trivial problems, while enjoy the fact that the real questions are there to be answered, but you may not see them answered in your lifetime. Otherwise, don't do a Ph.D. in theory directions.