Hi all, first post! I've been using emacs for about 8 years and org-mode for about 4-years (though I use org-mode without really "thinking like an org-mode user"), but there are a few things that continue to be annoying / make me feel uninformed. I wanted to "air out" the main inconvenience to see if there are some established solutions and learn new ways to think, and this community looks to be a good place to start!

The main problem is the following:

1. Often, I have a note (that can be a paper/book I read, or a conversation, or a life event) which I want to appear in several "views." This feels repetitive.
2. For example, in my "books.org" I might have a single line that said I read "Warren Buffett's guide to Making Money" in a chronological list of all books, but I also want my "money.org" to have an entry for this item, so when I go think about money I can remember the lessons learned in the book (maybe I also want this to belong to "psychology.org") . Furthermore, I might want my "diary.org" to have this book as a notable thing that happened to me (so I can e.g. review the most interesting things I read in 2021).
3. My current solution seems janky - I just make 2+ headers, one in each .org file. In each one I would have an entry called " ** <2021-03-23> Warren Buffett's guide to Making money", one of which is the "real" one that has my detailed notes from the book (say in money.org). Then for all the others I would add a pointer to the "real" one ith a link (something like " ** <2021-03-23> Warren Buffett's guide to Making Money -> [[money.org]](BLAH)")

Question: this is repetitive (involves copy/pasting) and seems somewhat like a hack. Is there a "best practice" to solve this situation?

A few scattered thoughts:

1. I'm happy if the solution is org-mode, but also more generally emacs and/or things that interface well with emacs.
2. I think the "best" answer would be if I set it up so that all these files were editing the same "thing" somehow. This is similar to [mirror/auto populate a section of text in another location in the same buffer/other file - Emacs Stack Exchange](https://emacs.stackexchange.com/questions/37032/mirror-auto-populate-a-section-of-text-in-another-location-in-the-same-buffer-ot), which had no answers.
3. One solution would just to have all of them point to the same file. But this creates a bunch of tiny files, which I find visually unappealing when I interact with my files at the file manager level. (e.g. Dropbox / Nautilus)
4. A solution that would solve 90% of my problems (which is definitely good enough right now) would be to tag each note with some tag, and then make it so that I can autogenerate something like "show me every note with the following tag I made in the last year" in a couple of keystrokes / a single elisp call. This seeeeeems like something I can/should do with agendas, but I haven't really grokked that and don't quite know where to start?

Thank you!