Got to have rules you know

I love to listen to the girls in their imaginative play. They were building a garage here for all of Erin's cars. As I listened to them they said now this one has to park here and he can't come out unless this one says its okay. And this one has to do this . . .

It's hilarious b/c they are constantly making rules but I am not sure they ever follow them. Why is it so fun to keep making up rules?