The one I have heard is about knowing more and more about less and less until you get to your PhD when you know everything about nothing
The common joke / cliché about the Ph.D. education is that, as your education progresses, you learn more and more about less and less until (when you graduate with your Ph.D.) you know
everything about nothing.
Finally he knows everything about nothing
It's much more impressive to be a Master of one trade than a Jack of all; there are very few employers who give recruiters a brief to find someone who knows a little bit about everything, but
everything about nothing.