I once knew a person who titled the first post in his blog, "A first post."
It was immediately pointed out to him that correct usage is "The first post." To that he responded: Well, every blog has its first post, and this post is no exception, so this is just a first post (among first posts of all blogs).
Neither that person nor the other people were native English speakers.
I wonder, does that rationale makes sense? How does "A first post" sound like for a native speaker?