I have never been in the US, but I always thought it's the personnel in embassies who are educated/qualified to check and (in)validate my visa documentation. On

I have never been in the US, but I always thought it's the personnel in embassies who are educated/qualified to check and (in)validate my visa documentation. Once on a border, they will only check that I'm not carrying anything illegal, and that's it. But the idea that my education/knowledge/experience will be checked again, that's weird to me.