It's good to share food with people who are hungry
Sara is about to order a pizza and her friend, who hasn't eaten all day, shows up to her house.
Sara wants to have enough pizza leftover for tomorrow.
Sara orders enough pizza to have some for later and to feed her friend.
Sara figures her friend will get her own food and orders only enough for herself.
Sara's friend eats for the first time in awhile and is satiated.
Sara's friend is now starving, wishing she could have some of the pizza.