I'm posting here my response to the following question:
I don't know if you're still into socionics, but I have actually become better in applying it, and I think it's pretty accurate. The problem is explaining the theory to other people. Socionics seems like more of a system that is based on observation than anything else. (For example, I can't see any reason why Ti types would necessarily seek out Fe types - you could come up with a reason, but it doesn't necessarily prove it, unfortunately.) That's why I'm wondering about its history, because it will make it easier for me to explain to people why it might work. So, here's the question: do you know how Ausra Augusta and her associates developed the system? Was it based on observing a handful of people she knew, or were, for example, hundreds of people talked to in order to develop Model A? (Or something else?) I don't really want to burden you with finding an answer, but you seem like one of the few people in the English speaking world who might know.
I still think of socionics regularly when meeting people and reflecting on their personalities. The subject, I think, will continue to interest me forever. I think the complementarity of functions that you mention is a great mystery that remains to be uncovered by science. Simply by giving the mystery a name (i.e. Ti and Fe), socionics does a lot towards finding an answer, but "Ti and Fe" itself is not the answer.
The answer is doubtless to be found in neurophysiology. Something about the neurophysiological activity known as "Ti" leads to neurochemical exhaustion if not supplemented by "Fe."
More broadly, any specific type or closely related types of mental activity will lead to exhaustion if engaged in long enough or with enough intensity (mirroring the effects of physical activity). As a result, one feels drained, irritable, or devoid of will.
"Ti" and "Fe" may be seen simply as convenient, though imperfect, ways of categorizing mental activity.
Since the source of "Ti" and "Fe" -- evolution -- acts via our physical survival and successful physical transfer of genes and is only interested in our mental activity inasmuch as it produces external results, the mental activity represented by "Ti" or "Fe" must also represent broad types of approaches towards dealing with one's external environment.
A "Ti person" tends to tackle problems and opportunities in his environment in a certain way that differentiates him from most others. This typically leads to success in some areas and deficiencies in others. Yet, because we are not bees or ants, the differentiation cannot be absolute. A "Ti person" who performs more types of tasks adequately probably stands a higher chance of reproducing than one who cannot.
The "purpose" of this differentiation appears to be to make social cooperation desirable and inevitable. It is distinct from sexual drives which make reproduction desirable or from survival drives which make animals territorial and prone to aggression.
The fact that what we call Ti and Fe tend to attract one another is a conclusion born of observation more than logical deduction. Augusta recognized that such patterns existed, but she had no name or framework for them until she came across Jung's Typology, which she adapted to fit her needs more closely. Model A was developed as a result of studying Jung, observing her acquaintances in everyday life, and discussing her ideas with a group of like-minded friends who took interest in the topic. They would field ideas among each other and see how well they played out among each other and in their personal experience, much like any informal but stable group of friends. In this way they were able to develop the overlapping experience that is so critical to socionics (as well as being its Achilles' heel). Without it, socionics discussions tend to be difficult and relatively unproductive.