Comment by cbhl

While I can't speak for the OP, I had been on the site for well over a year before I realized that you could search through past HN submissions at all (even though the search box is at the bottom of basically every page).

As far as I can tell, neither /submit nor the guidelines mention that you should do a search first before submitting.

Then, once you assume you should do a search before you submit, the idea is that such a search could happen on the same page as submit, as soon as you finish pasting a URL, and before you hit submit.

It's like when you go to a support site and type in a question, and it tries to give you answers by searching for other instances of that question (or by searching a knowledge base), before letting you make a new support ticket.