Well, I don't know how to start this one, since apparently I've thought of the same introductory sentence the last time. So this an opinion with a short introspection.
I've stumbled upon an interesting blog in which a geeky woman documents some of the online dating failures she has experienced. Overall it's not that different from what other women told me and given her high expectations (ie. being picky), I understand most of her commentary, since I've been told I'm picky too.
However few posts caught my attention, especially this one. While I don't know what either one of them had on their profiles, I think that she seriously overshot on this one (indirectly calling the guy a “douchebag”). Since I've read many of her posts in a short time (while in real life the individual events are weeks or month in between), I can see an obvious possibility why he essentially told her “no”. She'd repeatedly ignored a person who sent a message with poor grammar. And in this case I easily noticed a difference in his and her messages and the thing is that there are still many people who consider the lack of greeting and smiley faces poor grammar.
Another thing is that she has stated her mid-term life goal, which tells a lot about a person. Also, on a pragmatic note, being a geek into anything is still not cool outside of the particular subculture and sometimes not even inside. While studying IT, quite a few classmates told me that I'm weird because I like the theoretical stuff too.
And that leads me to the post title - while self-confidence is generally considered a good thing (or rather that it's bad when you have only little), I think it should be given out with a dose of skepticism against your own opinions. Whenever you become good at something, you also start being right about it most of the time and that over time erodes the innate sense of self-doubt and you tend to forget that sometimes you are not right. That doesn't mean that the other person is right in this case, but it's worthwhile to ask yourself why would that person think that he/she is right.