To me, a Con is a big scary place full of a whole bunch of people who don't want to talk to me. Perhaps some of those do want to talk, but they want to talk at me, not to me, as long as I make no attempt at speaking. And God help me if I bring up the fact that I write. From long experience, I know that when people hear that you wrote a book, they immidiately his psychic panic. They fear that you will immidiately lock them into a conversations where they'll be stuck, and they will do whatever it takes to either leave. If they wrote a book, their job becomes turning 100% of the conversation to their book, because once you talk about books, there can be only one.
Cons befuddle me doublely so because now I am walking this crazy line of a not-so-upwardly mobile novelist. That means that if I want to be on a panel talking about something, I need to have something that I can talk about. So, imagine me up on a stage with some other panelists doing my best to pretend that I'm an interesting person. What is there that I can talk about? How can I differentiate myself? Why would anyone even let me do that?
Could I talk about novel writing? All the writers do that. The back of the line starts across the street. "Hello, I've been a novelist for less time than anyone else, except for that person who sells 100x what I do, and I have the sales to prove it." That doesn't make for a great introduction. Such an intro sounds like, "Hello, I'm contestant number four. I am also a straight, white male who likes reading, fantasy, and walking on the beach. Did someone say Joseph Campbell?"
How about tech? I'm in the tech industry. I can surely talk about that. Yet, even that's useless. Unless one is a true giant in the industry, half the audience will match or exceed your expertise. And if you do start talking tech, that becomes an alpha-geek challenge. What you're really doing is whipping your dicks out and saying, "My time in the tech industry is bigger than yours is." Althought sometimes such talks turns into, "Yeah, I fucked with that corporation, too. Everyone's been in bed with that one."
For the life of me, there's no expertise that I have that is not readily surpassable with another guest.
As for fannish sub-cultures, I'm in an even-worse position. Should I talk about any fannish topic, due to my own sheer ignorance and their well justified calls of BS, I'd get clobbered by the audience. That route is beyond foolish.
I hope that I'm not sounding like a negativst here. I just truly and absolutely see myself as a bad fit for cons.