As humans, we like to tell the story about our past. It can be useful when trying to explain to the other humans and to ourselves just why we are the way we are.
We point to our past experiences as the basis for our reasoning.
We are the way we are because of what we observed, what we were directly taught and most importantly how we interpreted it. There were a multitude of variables that could not be predicted or controlled but it was up to our very young brains to make sense of it.
In case your are wondering or you care, this is the nurture side of the nurture/nature controversy.
Back in the caveman days, there were fewer variables and life was likely simpler. Good v bad, warm v cold, scary v safe, etc.
Our current world is far from simple. Yet the crazy part is that while times have changed, 12-year-olds today are still dealing with the same brain that their cave-child ancestor dealt with.