Because I Said So
The first thing that influences our perspective is our family of origin. When we are born, our parents are the gatekeepers to our perspective. They are Gandalf, guiding us into the world and explaining what is shameful and what is heroic. As we grow, siblings and close friends help shape our perspective as well.
The human brain continues to develop throughout the late-twenties. During that time, patterns of thinking are developed. These patterns form as behaviors are rewarded and punished, concepts are reinforced or shut down, and viewpoints are encouraged, berated, or dismissed.