The forgetting sense seems to actually depend in large part on stumbling upon the idea of remembering.
It's not so much that a spontaneous "hey this is the last chance to remember this", as much as it is that as I roam through my mind I think or remember the idea of remembering the thing.
From there it is as described in the earlier post: I can sorta feel the difference in strength or availability of the memory, and I have learned from extensive forgetting and introspection experience roughly how weak it has to be for my failure to rehearse it immediately or imminently to cause it to be lost.
But the nuance here, the discovery, is that practical "always on" use of the forgetting sense as advertised in that last post is an active skill, not a passive one:
the recognition that if I don't review it I will forget is passive - this is the essence of the "sense" part - but
the awareness that any given memory is about to expire, the opportunity to trigger the "sense" part, requires active cognition to "touch" the idea of having this memory, and to "reach" towards the memory just enough to get a feel for how readily it comes to mind.
This active part can of course be so deeply habitualized that it feels passive and automatic. You notice the awareness coming up but not the cognition that preceded it. This is why it took me so long to detect that there is an active component at all.
This also explains more thoroughly why memorization practice develops the forgetting sense - an explanation I previously found subtly lacking. It's not just that it gives you more experiences being on the cusp of forgetting and either rehearsing the memory or losing it! It's that it also habitualizes the creation of cognition snags for remembering!
I have countless little cognition snags all over my mind that cause me to think about things I am trying to memorize and whether or not I remember them. I invested so much thought, effort, time, and attachment into memorization, that over the years thoughts like that have habitualized. Now they are a regular feature of the language-free wakes/ripples of associations at the outskirts my conscious cognition.











