I've still got a bee in my bonnet (if I wore bonnets) about something Cory Doctorow told our class at Clarion. That you need to let the reader know the gender of your first person narrator up front, because it's something all people know about themselves, so it's being unfair to the reader not to let them know.

I may not have stated that exactly right, but that was certainly the gist of what I understood him to mean.

There's a number of things wrong with that. But the upshot is, I don't believe that's true of all stories or all characters. Some stories are better served with ambiguity or obfuscation. And some characters are more comfortable that way. At least in the beginning, when they're still building a relationship with the reader.

Sometimes the default isn't the dominant though. Sometimes the default is what the reader knows the writer to be.