E.g. I'd like to find an article on digital signal and processing which probably had the words like "signal" and "filter" in its text but all I can remember about the title used on HN is that it probably didn't feature either.
One tactic I use is to search on words in some comment I left in the discussion. If I search on my HN name, words I probably don't use overly much and check comments, I can frequently find it.
Sometimes, fiddling with the time frame helps. If I have some hand wavy idea of when I read it and not enough other info, I will resort to playing with that element of the search engine.
It's tedious, but sometimes results in successfully finding what I was looking for.
I've always wished HN had tags...
signal filter "http://" site:news.ycombinator.com
For example lets open the main page, there is a "Microplastics found in 93% of bottled water tested in global study" title on it. Click on it and you'll get to the https://www.cbc.ca/news/technology/bottled-water-microplasti... page. Within the article text it mentions "major national brands across Asia, Africa, Europe and the Americas". In this example I would like to search for "Africa" (which is not mentioned in the commentaries) and find this article as one of articles posted on HN and mentioning Africa.