From a thought model point of view, I couldnt imagine that a regular human being could lack any of the 8 functions. In some way of interpretation he should experience them all through the course of his life. Because his 4 functions (if there are 4) would be basically the same like the four shadows, yet grounded on different variations of appearance.
Therefore a tertiary or inferior function would make sense, given the premisse that a human being uses all of the 8 functions in his life.
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From a more practical and life-oriented view, I can say that the third function is often strong in many people.
Be it my INFJ girlfriend wanting to fly a helicopter or experiencing the thrill of climbing a wall for no apparent reason.
Be it my father being a brutal enforcer of logic ISTP, wanting harmony for the herd and holding the family together, reacting to basic death-proof morales totally defieng his strong logic and opinion on things, when he hears the calling.
Be it me listening to a three hour conversation of totally random girls, just for sheer politeness, totally loosing my mind in the process, developing multiple serious headaches.
Be it my sister an ESFJ getting caught in my wake of ideas from time to time, suddenly deciding to be intrested in something completly new, even if she has not a single clue about the complexity of the new thing she discovered.
Be it my mom an ISFJ totally grounded in her feelings, morally a tradition roller, no high-risk taker and seemingly misunderstood, suddenly become attracted to one of my dumbest ideas, like buying a banana tree, laughing about my cruelest of jokes, though they disrespect any sort of tradition.
Be it my ISTJ buddy, who is a total strategist with no respect for any human life, except his own aquisition of wealth, needing every thursday evening his round of close friends, or else he will get depressed, masking it naturally through false pretense.
Be it my unholy *may the devil get her* ex-girl an ENFP, who never EVER ended on giving me lectures, how to organize my things better, while her own things were a mess from heaven to hell.
Ok, I guess that's it.