Another way to look at it is the number of different jobs a certain person could do, if necessary. A surgeon can operate, but if needed, also likely fill in as

Another way to look at it is the number of different jobs a certain person could do, if necessary. A surgeon can operate, but if needed, also likely fill in as a nurse, CNA, phlebotomist, and could of course sterilize a room. That's not to diminish the contributions of any particular group but not all individual skill sets are created equal because some (literally) encompass many others.