The final statement is that once you become the lead renowned person in the field, for instance, in the field of cardiology (like Eric Topol), you become the reference. Folks as big as that, with that much weight behind their name, with that much reliability, are able to make broad statements without really having to provide an arsenal of support. Most of them still do out of courtsey for academic excellence. So one day when you are the top historian on Afghanistan, people will reference you.