The way I see it, all of us have the whole of a "socion" in our brains. If we had infinite amounts of time at our disposal it would be possible to derive all there is to know from a single brain's interaction with reality. The thing is, there isn't a lot of time available to us, and it is required of us that we act efficiently (time-efficiently considering time is the only basic commodity in psychology) in order to survive. Hence why we have to prioritize and exalt one of our "types" above the others. And that's how the repression and dominance of functions emerges. Fast forward to Jung and you've got the birth of socionics.

There isn't just 1 type, though. There's at least three levels on which the type phenomenom manifests. There's the political attitude and leadership style of the upper type, the societal role (job) of the middle type (which socionics discusses) and the concrete action style of the lower type. Each of the levels has it's own quadras, functions and intertype-relations. And that's probably only the beginning of the complexity.