I use the analogy of Russian dolls with secret messages inside them. You don't know how many dolls there are and you can only ever open the doll that was inten

I use the analogy of Russian dolls with secret messages inside them. You don't know how many dolls there are and you can only ever open the doll that was intended for you. The secret message either contains instructions for what to do, or who to pass the dolls to next.