It's good to show your appreciation to people.
It's Sandra's birthday, and she gets a new toy from her father.
Sandra wants to play with her new toy.
Sandra thanks her father for the present then enjoys playing with her new toy.
Sandra runs of to her room to play with her new toy without thanking her father for the birthday gift.
Sandra's farther feels that his gift is appreciated and is happy.
Sandra's father is offended that she didn't show any gratitude for his thoughtful gift.