Isn't this directly against WP:NOR, specifically WP:TERTIARY? Every fact must be supported by reliable first-party source, and the idea's provenance is that source.

In the research, there are often long paths that lead to the ideas: lunch room conversation -> paper 1 -> web search on term seen -> paper 2 -> web search on another term seen -> wikipedia page -> another wikipedia page -> original source (paper 3) -> paper 3's citation list -> paper 4 -> fact for your own paper

We always cite only the very last item in the chain, paper 4. I'd might cite other papers I've seen, but only if they are relevant. I was taught that the tertiary sources, like encyclopedias, are never to be cited, unless they have original facts which cannot be traced to other sources.

In my opinion, if you used Wikipedia, you should cite it. If you instead got your idea from "lunch room conversation", or a private email, or whatever, you can also cite that. It's a really huge problem that people pull ideas from Wikipedia, attribute them to something like "paper 4", but then it turns out that what Wikipedia said and what papers 3 and 4 said were not the same, and what Wikipedia said was actually based on some other paper 5 that turns out to be a bunch of bullshit, or a Wikipedia author made it up and wrongly attributed it to paper 3, or a Wikipedia author didn't understand paper 3 and made a total hash of it. Etc.

This of course also happens plenty when Wikipedia isn't involved, but for whatever reason people seem to have the mistaken idea that citing Wikipedia is inherently bad. There's no rule against citing Wikipedia, or tertiary sources in general, from professional work.

When a later person (e.g. a scholar or Wikipedia author) is trying to understand your work, it's incredibly helpful to know where some claim or idea came from. Otherwise they have to jump through extra hoops to trace the actual attributions and figure out where mistakes came from.

Wikipedia's original research policy is not relevant to what works you should cite in academic papers. A Wikipedia article is not supposed to contain the original research of its authors, because it's the wrong venue for such work, and because when such material is added it typically turns out to be nonsense or spam, but rejecting it on the grounds that it is unsourced is much easier.