Isn't it reasonable to be confused and ignorant being a learner? I jolly well know that I need exposure, but I can't help it if I don't get it at this stage.
I think you're misunderstanding me here. I'm not attacking you for lack of experience and exposure or saying it's unreasonable, and honestly have no idea why you're getting this impression. I'm just pointing out that there is a difference between grammar points that you can be expected to memorize 100%, grasp, and internalize before moving on (e.g. conjugating the -te form of verbs, fundamental particle usage, etc.) and other points that you probably won't be able to fully master without considerable (sometimes even years) of exposure. For the latter, sometimes it is best to understand them as best you can, file them away in a compartment of your brain, and then move on and try to observe in the future. If you don't learn to do this, you run the risk of over-obsessing about relatively minor details at the risk of learning more fundamentally important points.
I'm aware there could be subtle difference and that's why I ask. I also understand that sometimes it is difficult even for a native speaker to explain the difference. I just ask, if I get a good response I'm lucky, if not I wouldn't dwell on it.
And I gave you an answer, didn't I? To be perfectly honest, I enjoyed answering your questions at first, because you struck me as one of the more thoughtful and serious learners on this board in a while. I may have to retreat back to the sidelines, however, as it seems that you find my responses lacking, given that you never comment on the substance of what I say, and only seem to get upset at how I say it.
And I'm pretty sure I said this before, but I'm not a native speaker of Japanese. I'm an English native who went through the same learning process you're going through now (albeit some time ago), and the primary reason I'm responding is because I'd like to think I have some insight that can help you in grasping these concepts.
edited to add the following
What is this in terms of grammar?
It's an old person/dialectal version of ~のだ, or the "explanatory/contextual の" as it's sometimes called. It appears as (~のです/~んです、~のだ/~んだ)in standard modern Japanese.