As someone trained in IT, having spent 15+ years as a network consultant, it sometimes surprises me that people expect you to be an expert in other areas of IT. I know networks and subnets, protocols, infrastructure, network security, data packets, switching, wireless and related things - that was my expertise (until I changed direction a few years ago). But people expect an IT person to also be expert in MS Office, Linux, Multimedia, Mac, telephony, databases, computer circuitry, business packages, etc. And while I know a lot about those things, they are not my field of expertise. Is it the same within specific fields of science? Is a cosmologist more expert in one area of cosmology than another area of cosmology? I imagine there are physicist with expertise in different areas. Do biologists often find themselves explaining that the area of inquiry is not in their field of expertise?