In this case it's an excerpt of a larger post that I was writing while I ran into this.

I don't think there is a good single-sentence title that would encapsulate the whole thing without being an already well-known fact, like say "Header include order matters".

Also, I wrote this one as a narrative, not revealing the conclusion at the start - basically a reconstructed version of how I encountered it myself. I don't write all my posts like that and it's not for everyone: but once I've decided on that, it makes no sense to reveal the conclusion in the title, I think?

The HN headline could be changed though if it places a priority on information-full titles.