1. We only dream of people we already know.
Our minds can not discover new faces. In our dreams we see real faces, real people that we have seen during our life but do not know or do not remember them. We have all seen hundreds of thousands of faces throughout our lives, so we have an endless supply of characters our brain to utilize during our dreams.
2. We forget 90% of our Dreams
Within five minutes after you wake up half of your dream is forgotten. Within 10 minutes you forget 90%.