I've always found this part of the MBTI/Jung theory confusing/confounding.
The brain is very complex .. how can it possibly be abstracted away with 4 aspect (I mean cognitive functions) that have a very well defined mathematical relationship?
Why is it that a function is always paired with its opposite? (i.e. Ti/Fe)
Why is the attitude of the auxiliary always the opposite of the dominant?
How can all the complexities of the psyche be encapsulated in so few aspects?
Plenty of the people who are "too much" into the actual Jungian theory tend to look down on the MBTI for turning that elegant structure into a "sliding scale" of traits. But if you think about it, a sliding scale of orthogonal traits makes much more sense as an abstraction, because you're not making any assumptions about what's going on inside; you're only measuring different aspects of the personality without making any assumptions about how they relate to each other.