This reminds me of how I met Nate Soares. He came to a few LessWrong meetups (his first ones), and I dismissed him because he was talking about a bunch of technical things that didn't seem very interesting to me. (I've was much more interested in finding flaws in my own emotional thinking then in discussing things like many worlds quantum mechanics or decision theory.)

I wrote him off as not-a-very-interesting person. Some of it was his interests, I was also a little offput by his intensity and took it as a sign of bad social skills. These days I read and re-read his blog and have gotten enormous gains from doing so, and he's off doing wonderful things.