Dr. arcia studies the development of emotions. he has observed that it is not until a child is in preschool that children develop a sense of guilt. dr. arcia is interested in

I believe the answer is social development
social development refers to the discipline that aimed to improve the well-being of individuals when they're interacting with their social groups.
A sense of guilt is really important in social development because it allow us to sympathize with other people and form a close/personal relationship with them.

It’s because it’s was very fun