alt Hacker NewsI see, maybe my use of “romaji” is sloppy because I implied “Hepburn romaji” specifically because that’s what I chose in the article. I do explicitly mention that other romanizations exist and that I chose not to use them — so I’m not worried about misleading someone who reads the article. But on pedantic level I see why “si doesn’t exist” sounds overly broad.
I think also that anyone who's spoken Japanese for a while already has internalized that "si" === "shi" because there literally isn't the sound "si" in modern Japanese, as the other commenters mentioned it's often romanized both as "si" and "shi" in daily life, if you typed "si" into a keyboard it renders し, it goes on. The original comment on this thread includes one such person who literally didn't follow why "si" is wrong, and I felt the same way too as a long-time Japanese learner. It's a very "copy paste Western language concepts onto Japanese" way of conceptualizing the language, which is IMO a great way to set oneself up for great struggles when trying to learn a language that is structurally different, because it's not the right mental model.