Sometime recently I read some article where Feynman talked about how he got to a point where he basically gave up and considered himself a failure. From the excerpt he talked about just not being able to keep up with all the research and grasp all of the new ideas, as a result just feeling like a failure. What he did next, was the interesting bit though. He accepted it. He basically thought “ok, well, I don’t care. The only reason I do physics is because it’s interesting and fun. As long as I can keep doing physics I’m happy”.
The next day, he went in to work, saw a workmate spinning a plate on a stick and thought about the motion and whether it could be described with an equation. He spent the rest of the day working out an equation for the movement of a “plate being juggled on a stick”. He found this extremely interesting and satisfying. Moreover, he got to focus on the details (as opposed to large abstractions) and solve a problem from start to finish.
From the plate, he moved onto another interesting problem, then another, until it turned out he was solving lots of really important problems.
The point is, don’t lose sight of what you really love and why you started. Also, if you find yourself in a place where it’s not fun/interesting/fulfilling anymore, maybe you should stop and try to remember what it is you were after in the first place.
Link to story: http://www.physics.ohio-state.edu/~kilcup/262/feynman.html