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.
signal filter "http://" site:news.ycombinator.com
You will need some variations, like including "https://", but this is a good start.