Upon realizing many patterns in the types, it seems that the Extroverted functions quite literally take on the nature of immersion, and the Introverted functions quite literally take on the nature of reflection, and they do so by existing in a duality as two sides of the same process: Fi-Te, Ti-Fe, Ni-Se, Si-Ne.
We'll make a contrast first between the literally opposite perspectives, Ne/Si vs Ni/Se. Ni/Se types handle reality in a way that may seem stranger to Ne/Si, but it's all in perspective. Se takes a quite literal account of what's happening without any reading into a situation, so the Ni/Se type could find themselves often saying to the Ne type, "you know, that might be what's happening, I didn't see that, you're probably right" or "I'm skeptical of jumping to that conclusion." Ni's aim has always been different from seeing patterns externally and in dynamics, as it receives
raw data from Se without anything added, then retreats inwardly to reflect in an abstract unapplied way, sometimes for days, but it never acts like Ne/Si by making frequent hunches/assumptions of externals (Ne) and reading into things sometimes as an ingenious talent of External Intuition, then Si accessing memory to see if it really has been so, or what other external possibilities there could be extrapolated from experience (Si.) This exact latter process, in a nutshell, seems like it
should be the default process of a human, to realize the explicit truth and workings of things happening, but it is actually the opposite process of an Ni/Se type, whose daily obsession is not about matching up abstract external hunches with a sea of inner concrete data/experience, but about finding implicit deeper truth and meaning from a reflection of raw sensation of reality.
Instead, Ni takes an enlongated, philosophical and impilcit approach to understanding reality, and Se sees and immerses fully into raw data as it is, so comfortably in-the-moment without wandering or putting much together but an appreciation of rawness (Se.) But once it latches firmly onto a big-picture concept that shocks oneself, it doesn't apply it specifically and say "see, here is the concrete proof of what's going on now (Ne/Si.) I solved it!" It instead solves a situation by interpreting it within its larger web of perception, "I solved what this
means to me" or "what it could imply in a subject" (Ni out of context due to being anti-external) as it retreats deeper into its ideations of what a certain reality might entail as a bigger idea or truth, and over what personal lesson it takes away into the rest of their day's reflection (Ni.) It isn't explicitly applied to solve or conceive of what's really happening, like an Ne/Si does through seeing external patterns and imagery: The Ne/Si type goes into reflection by accessing all concrete data and information they know to be true (Si) so precisely without muddling it with abstract leaps unrelated to the moment, like Ni does, and where they shine is through seeing what really is behind a moment (Ne), reading dynamics and minds, seeing so easily the underlying patterns, something Ni is disinterested/shied away from, as, for Ni, these ideas are not internal and general enough to be applied to a slow pace of reflection upon a bigger-picture conceptual philosophy, or lessons and generalities about subjects and life (Ni.) We use all the functions to a degree.
The definitions of the processes Ne, Ni, Se, Si are precisely,
Intuition of Immersion, Intuition of Reflection, Sensing of Immersion, and Sensing of Reflection. We know the latter two as accurately defined in MBTI: Immersion (Se) and Memory (Si,) but they got it wrong on the first two, and neither of these four in total have anything to do with J vs P lifestyles.
Fi-Te and Ti-Fe work in this same pattern of duality, of internal reflection to external immersion, back-and-forth, as one function makes up the internal life, and the other makes up the external application. And we know, we also less frequently use the process opposite to ours, when we need to learn more, but it's not our default pose.