So the entire ISTJ for us it setup ahead of time, and our beliefs follow as we go through life?
If thats not correct explain a bit more, I'm trying to follow
Not exactly setup ahead of time, but predisposed as in a tendency to be a particular type. Barring any cataclysmic event in our life, as our brain develops, these tendencies become firmer or weaker through social molding.
Early influences and stimuli impact our brains development, fine-tuning, if you will, our tendencies toward certain behaviors. A wise parent can recognize some of these tendencies and work with the child, providing stimuli that will counteract or reinforce the behavior, as desired. The tendency is still there, but the magnitude of that tendency can be encouraged or reduced.
My most recent example has been Chamberlain. I picked him from the litter because he appeared more independent and not nearly so tied to mom. However, this began to work against me right away, as he showed that he did not prefer a lot of cuddling or snuggling. Recognizing this, I worked with him, making sure that I touched and handled him constantly. I prepared him for his first vet visit by touching him repeatedly, sticking my finger in his ears, holding his mouth open, looking closely into his eyes with a flash light, picking up his paws, his tail, and all other methods of touching and preparing. I also took him with me everywhere, so he became more used to unusual sights, sounds, and smells. So the vet visits have gone ok, he's a bit territorial, but otherwise seems pretty well adjusted.
However, while he does tolerate lots of hugs, belly rubs, baths, and touching in general, there is no doubt that he is uncomfortable with anyone placing their hand on him for a long period. He doesn't like laying on people and he doesn't want any part of your body laying on him. Had I left him alone, there is little doubt that he would have been completely stand offish and would not have tolerated near as much cuddling and hands touching him as he now does. It is clear that he enjoys petting, but that he has a definite idea when it should be over. That is that same independent streak he has always had.
Similarly, I believe we are wired to be our personality type. However, outside stimuli and interaction with others can certainly affect how strong our preferences are in our personality type. I believe this is why we have all ISTJs preferring no hugs from strangers or people that we don't know that well, but each of us having a different tolerance level. Some of us, this can almost ruin our day, while others of us just give a quick squeeze and never really give it a second thought.
Srsly, I could be all wet...but this is my belief as to how it possibly develops. I do know that very young children show definite preferences and personality traits.