None in particular. I was talking about "primary sources" as a category. See also what I wrote here:

https://news.ycombinator.com/item?id=47178573

It was a meta point. Sorry if I gave you the impression that I was weighing in on the particulars of jmyeet's essay. Rather, it was a high-level point that if you know a ton of little facts but you're only seeing half of the story, then you need to improve and broaden out your intake.

I would have the same opinion of a poster who was so one-sidedly pro-America and anti-China.

The good books, unlike the good podcasts, can rarely be reduced to a single forum comment. You don't read them to cite them as a zinger in an online back-and-forth. You read lots of them, and you cross-reference them with the world around you, to slowly build up a view of the world that's irreducibly complex. You read them to escape yourself and your times -- the exact opposite of "navel gazing", in a sense.

Most books add to "the shared pool [of] meaning", as you say. Pick any one; I didn't have a specific one in mind. The commenter to whom I was responding is in a state where pretty much any well-written book about history would help them out a lot. Something written before 1980 might be especially illuminating.

It might take many books, if they want their comprehension of history to actually be "hardcore".