Ya, I had similar thoughts. In fact, I am also a PhD candidate and I spend my whole career in one field but my problem is I am not really good in basics too. I got education from Nepal, from USA but things don’t improve. The thing is the world had become so big and the subject matters are so vague, for me I think I am most Dum guy, but still a PhD student. I don't know, I am doing PhD in general school and I am always laughing what to do with my phd where to go.  All the Caltech, ucberkley, Stanford, with all the good school come to our school to teach but the people like us where to go. Any way, again to the point, don't worry, I am in your line, I feel I don't know anything even if I am a PhD student, at least you think you know little bit in your subject matter but I think I don't know anything but life goes on. Ha Ha