Is this a phenomena in philosophy, that the more you study the more tricky basic questions are to understand, not just answer? I'm not sure.
Can imagine it in science, if not math.
Coding is probably a good example of a skill-set in which one forgets things and this extends to even working out what's going on. Or, perhaps, esoteric religion (what do my students even want from me?)
I mean, oddly, both these seem to fall under 'function' or 'purpose', not the essence of understanding.