I agree 100% on the "line of sight" strategy being a really effective for developing music skills. I do the exact same myself. But I actually have had a bit of success with doing the same with books on a well-curated bookshelf in close proximity. It definitely works best for reference books, but almost anything that's a primary source works great for this. I often mark these books up with notes in margins, underlines, sometimes even sticky notes. If I have a lot to think about, I'll write that in a leuchterm notebook I keep on the same shelf, and just put the notebook page number in the book margins so I can go back later. When I go back to them - I'm not just able to build of of the original work, I'm able to build off of my own previous thoughts and easily recall my own situations where this applied. It's honestly really satisfying.
Some examples of books I keep going back to many times over and still find valuable as someone with ADHD:
- "The Art of War" by Sun Tzu - Any time I'm on any kind of competitive game kick or just thinking about competing in general, I always find something applicable to my situation. It's super short too.
- Wolfram's "A New Kind of Science" - it's massive and not something I could ever read straight through - but it's so dense with interesting applications of a super simple concept (and great images of those applications), I can jump between the chapters and get something interesting to chew on every time.
- "The Federalist Papers", and also "The anti-federalist papers": They're great from a "oh, so this is why America is set up like this" perspective, and also from a "Let's see how close or off these guys were from predicting the future on specific topics! (ie, economic and social predictions mostly). I also like that the English used is not actually terribly hard to understand, despite being older.
- "Learn to Read New Testament Greek" - Really great smaller intro book to Koine greek with good exercises inline. Greek is one of those languages that shows up in so many places, that it's really satisfying to see it in historical perspective and then learn to recognize it elsewhere. This book also scratches some of my personal interests around the history of early christianity.
I also do the same process for some religious texts (New Testament and Nag Hammadi Scriptures).
Just as you said, things that require pure diligence don't usually work out for people with ADHD, but some books out there are straight up great for dopamine if you can find them. I think the core tings to look for are:
1. Super information dense yet still good for jumping around and digesting small pieces. You shouldn't have to re-learn the core premise every time.
2. Should feel different and novel when you come back to them after time away. Some of the greatest writers, especially philosopher-types, express ideas in an intentionally ambiguous way. They ensure that a part of their intended meaning is accessible to anybody on first read - but the more complete interpretation requires some degree of context and re-reading. A reader's interpretations of texts like that change and grow based on their own life experiences, and as a result it often feels like you are finding new things each time.