Holy shit. Brainfart. Just a jumble of words to me, with the ocassional "objective" and "subjective" scattered about.
Basically Si is not just what it is, it is the sensing object, but with a deep sense of how the object "should be" attached to it, so in essence the Si dom can drive others mad with his nit-picking in his quest to make things "just right" for himself (like Goldilocks with the Three Bears), but not necessarily out of a sense of maliciousness; however, this is why SJs can be perceived as "critical" (and well sometimes they are, but that criticism tends to be exercised by Fe or Te upon others, making ESxJs more bothersome to some types) ...however, the ISxJ still has a perception of what should be properly contained and so forth, and if he makes this too apparent, other people can get irritated and mistreat him or her, and being an introvert and not a dominant judger, they can accept this "abuse" passively, only resisting with a seemingly surprising extreme stubbornness.
And maybe you can get through this part, untouched, as I believe it is quite important (it shows how Si and Ni are equally symbolic, but the Si type accepts the symbolism as reality, while the Ni type creates symbolism to represent reality):
Actually he moves in a mythological world, where men animals, railways, houses, rivers, and mountains appear partly as benevolent deities and partly as malevolent demons. That thus they, appear to him never enters his mind, although their effect upon his judgments and acts can bear no other interpretation. He judges and acts as though he had such powers to deal with; but this begins to strike him only when he discovers that his sensations are totally different from reality. If his tendency is to reason objectively, he will sense this difference as morbid; but if, on the other hand, he remains faithful to his irrationality, and is prepared to grant his sensation reality value, the objective world will appear a mere make-belief and a comedy. Only in extreme cases, however, is this dilemma reached. As a rule, the individual acquiesces in his isolation and in the banality of the reality, which, however, he unconsciously treats archaically.
It's hard for me to separate Si from Fi, realistically, in people though. Like being close to high Fi ISTJ I see just how particular his tastes and how deeply impressed upon him and refined they are. But unlike the INFP who puts stock in the ego of their Fi preferences and may think these particular tastes make them so special and misunderstood and sensitive, the high Fi ISTJ is just quietly but stubbornly solid and secure in the "rightness" of his preferences, because Si is concerned with a subjective "correctness."
Both can come across as pretentious as fuck to someone who doesn't agree with them, but to someone who understands or agrees in generalities with their peculiarities of taste, it can seem like a deep and admirable trait, a real talent for the aesthetic. I think this is why Jung says Si doms have great potential to be artists (despite Keirsey calling ISFP the artists).
Jung's definition says NOTHING about memory, but I believe the association with memory comes from what he refers to as the archetypical or mythical subconscious projection on to the object, which naturally comes from one's personal past experiences, herp derp derp, and this may create preferences or patterns that are repeated because they feel "just so" to Si.
But it's not strictly about memory or memorization, no.
