Why Many People Don't Change - That many people don't change throughout their life is no surprise to most and the reason for this lies in the complex survival mechanism of early infancy. During the earliest days of life, negative and positive valances for experiences are created. Positive valances are for experiences during which needs are met, as when their mother feeds them when they are hungry. Negative valances are for the opposite, created when critical needs go unfulfilled or when they experience anxiety while gaining fulfillment of a positive need.
We now know that infants are far more capable than had been believed, even capable of understanding certain simple arithmetic operations. Being wholly dependent, they are especially attuned to the emotions of their caregiver, especially when they are anxious. Thus, if the infant senses their mother's anxiety when seeking nurturance, this experience willcreate a powerful negative valence, a Pavlovian-type conditioned reflex behavior that will exist and affect their search for intimacy throughout their life.
Another critical factor is the infant's tendency to view situations in black/white terms, whether an interaction is satisfying or not. Thankfully, for most people this tendency becomes modified during the course of development as youth and adults increasingly understand that most interactions are shades of gray rather than an absolute.
But just as the ripping up and rebuilding a road is difficult and time consuming so too does the change required to modify a fixed personality structure. Which will not be necessary so long as the child has experienced a good enough parenting experience, which need not be a perfect pairing experience for none ever experience this.