Introduction: I think of personality as a person's particular combination of thoughts, emotions, and behaviors. Since emotion is the driving force behind human thought and behavior, personality is mostly determined a person's emotional makeup. Children acquire their emotional makeup mostly* from the people whose faces are imprinted in them. The entire process is reactive. No emotion is acquired consciously.

How category 1 and 2 emotions are acquired during childhood:

(Note: In the paragraphs below, parents refers only to people whose faces are imprinted in the child. If a biological parent's face is not imprinted, then that person is not considered a parent in the following paragraphs.) 

1. When a child observes a person whose face is imprinted expressing category 1 and/or 2 emotions in response to a situation and the emotion is not directed at the child, the child will learn to respond with similar emotion in similar situations.

2.  When a person whose face is imprinted directs category 1 and/or 2 emotion toward a child, the child will learn to respond with the opposite* emotion in similar situations.

Children typically experience the emotions of people whose faces are imprinted in both ways described above.

Children typically acquire emotion preferentially from same sex people whose faces are imprinted.

Since children typically spend more time observing than interacting with people whose faces are imprinted, they typically end up being more similar than different to the people whose faces are imprinted. 

During adolescence, the ability to acquire emotions as described above stops completely and never returns. Once a child becomes an adult, their emotional makeup only changes as a result of aging or brain injury.

*In this context, category 1 and 2 emotions are opposites.