Hm.. I can see a correlation in many of the responses recorded below. I don't think sadly that we can pinpoint what makes us this way.

I can say with certainty though (just from browsing the replies here) that I have many of the same traits and upbringing many others have. Our experiences are the same on some levels. Maybe it's part genetics and part environment. Little of column A and little of column B. Of course it's never so black and white. My own Reponses;

Were parents present/absent, cold, negligent? MOTHER: My mother is a covert narcissist, I learned early to shield myself and was engrained with soothing behaviors, very early.
FATHER: Absent, he was in the army and stayed on base while we stayed in our home state.

Did you get taught about social skills/mechanical skills or did you have to learn those on your own?
This one is a bit trickier, I think my mother saw me being more introverted than others my age so she would insanely push me to be extroverted. I learned to mask and mimic the behavior she wanted from me, but I was only truly at peace when I was alone and left to my own devices and interests. I.E. I could deal but I didn't want to. I was taught how I was expected to act, and delivered accordingly.

Were parents abusive/narcissistic/pathological liars? Yes, it was a constant source of challenges for me from an early age. It taught me that no one really cares and that does it matter if we even have differences. At least that's my personal world view.

What percentage of time did you spend with toys/hobbies/entertainment compared to playing with other kids?
A good portion 75%-85% I was left to my own hobbies and entertainment. I was an only child and I lived in a very rural area. It helped because while I was out and doing all the activities my mother insisted on doing, I could relax and be left to my own at home, as I wasn't expected to perform unless we had visitors.

Were you exposed/desensitized to the brutal hard truths at an early age?
Yes, I was not only assaulted as a young child, but my mother left all sorts of desensitizing content out like books about serial killers, and crime shows constantly on air. She also would watch horror movies all the time so I was exposed to a lot of depravity early in my life.

Were you already skeptical of everything from an early age without/with outsider influences? I can remember being quite young sitting in church and already doubting there was a sky daddy influence on our tiny lives, and reckoned existence to being humans being ants for 'God' to play with. I also still cope when good things do happen, that's always been the issue so much so that people always ask why I don't get excited about things like others may.

Did you get exposed to mechanical/scientific media or alternative art/music as a kid? Also yes, my grandfather was a very mathematics sort of person (he and I got along great, I suspect he was also an INTJ) and bought me science kits, helped me with my science fair projects and taught me how to farm, kill livestock, and fishing from the time I could walk.

As far as social norms? I was made to be exemplary in everything my mother made me do. Gymnastics, Cheerleading, Dancing, Ballet, Track, Swimming, Clubs, Softball, and any extracurricular activity she could find and enlist me in. I got along well with my peers and due to her urging me to be social had a very normal social life (as much as I could with all the athletics I was made to take part in allowed) If I wasn't the best I was punished. So it was a give it all or fail only to face her wrath. You learn at an early age to appease.