In my case, it's because my best-fit type doesn't fit all that well. The closest thing I've come to is INFP, but I don't feel much kinship with other INFPs for the most part. And I'm the most T in my family-- which isn't saying much, but it skews my perspective. Basically I don't think I'm capable of objectivity so I reserve judgment.
Also I kind of like being an enigma, wrapped in a riddle, shrouded in mystery.
Sweet, then you know how I feel! Or think? Heh.
Well, anyway, I guess I will just have to do more research to see what I am. Self-knoweldge is essential.
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Kiersey couldn't use functional analysis because some types that have opposite cognitive processes are not opposite temperaments.
For instance: The opposite of the ENTJs' cognitive processes (Te Ni Se Fi) is ISFP (Fi Se Ni Te) but the opposite of it's temperament (abstract utilitarian) is not the ISFP temperament (concrete utilitarian), it's concrete cooperator.
I put myself as ISFJ/INFJ because I can relate to some descriptions of both of them(compared to all other types those two resemble me best)... although I do lean more towards N I think. However I don't relate to Everything that is in one or the other, it's like alittle of both... so why can't I put both of them in? o.O I don't really see why someone has to be completely one type and expect them to be everything it describes them to be. We are not clones o.o but w/e it's not a huge deal to me >.>. I like both! so hah!
"To the world you may be just one person, but to one person you may be the world."
^Keirsey decided to avoid the problem because temperament is observable while function use isn't, necessarily.
I don't think they're that different. Temperament is just more holistic and harder to falsify because you're going from generals to particulars. Any outliers can be lumped into 'things that aren't MBTI'.