The circular flow of economics

My mother, her boyfriend, and I work at Pizza Hut. We want to buy things to make living possible so we want to pay for example electricity and groceries. In order to get these groceries and pay for the electricity bill we all need to perform services for the Pizza Hut franchise. In order for the customer to get their pizza, Pizza Hut needs workers to give it to them in a timely manner and make a quality product. For my family to survive and to get the things we want, we need to perform these services. The customer pays Pizza Hut for the pizza they wanted. So to get the customer their pizza Pizza Hut pays workers and the workers do the services required as an employee to purchase what they want. So my family fits in by doing these services so we can buy products we need for survival.

We've learned about rational self interest. Many people see this term as a person being "selfish" but the term refers to a person looking at how to benefit their interest to the fullest extent. Usually we can see this term in society for example when I went to Chicago this past weekend with my family there were a lot of homeless people asking for change while people were passing by. Several people said "No" that they wouldn't spare some change. The change they have could eventually add up to paying the tolls, rent, or food expense. So because there is a benefit to keeping that change, the people refusing to give out change are benefiting their self interest because the marginal cost doesn't outweigh the marginal benefit of using that change for something for their interest.