I've felt that there are students who are just incapable of making relatively simple mental models of the concepts that we discuss. Just because this seems to

I've felt that there are students who are just incapable of making relatively simple mental models of the concepts that we discuss. Just because this seems to be the case, I would only ask that you don't let this become a limiting belief that you project on your "incapable" students. I only say so because I know I've taken various courses over the years (HS or college) where that sort of analogous big-picture communication you're talking about didn't really click for a few months or even years. When one is overwhelmed - or at least feeling overwhelmed - with the volume of new fundamental concepts to be grasped, it's akin to having 1,000 jigsaw pieces dumped on your coffee table. Oh and by the way, we're going to apply time pressure and grade you on your ability to figure out the big picture. In that case, learning can turn into a fear-based "tread water because I'm drowning" activity where rote memorization is the fallback tool to get the learner to shore alive. The outcome is no longer the joy of understanding and meditating on those analogies/models to get the fundamentals to click, but trying to avoid death (err, a failing grade). It wasn't until I revisited those certain topics later without the time-sensitive pressure of exams/grades that the broader models for understanding would "click" and all those rotely memorized fundamentals would fall into place - which is an indescribable joy. So while your incapable students may not seem to grasp the big picture now, it's likely you are still making a difference by implanting those fundamentals which will snap together later on in life.