You should share things with your partner.
Mark is eating in the cafeteria and his friend forgot his lunch and is upset.
Mark wants to help his friend eat lunch.
Mark decides to share his food with his friend, by splitting his meal.
Mark asks other if they have food they can give his friend to eat.
Mark is happy he gets food, and they both enjoy a good conversation.
Mark's friend feels weirded out that Mark doesn't share and Mark feels selfish.