In 1996 I took a TCP class in Chicago for which it turned out I was overqualified; it was mainly how to use tools like telnet and FTP.

But what I remember most: the two other students were mainframe programmers, and they were just as baffled by my world as I was by theirs. It really was an entirely different computing paradigm, although 30 years later I probably have enough experience to make more connections than I could then.