Sometimes we experience unfamiliar faces in our dream, as paradoxical as it may sounds we only experience things we know in our dreams.
Try to think about how many faces you have seen the last time you went out the door, i can quickly come over one hundred. Every face we see is imprinted in our subcuncius.
In our daily life, the brain quickly discards unnecessary informations. But as we go to sleep, our brain processes what we have seen and done, thereby pulling forth some of the faces we have seen throughout time.
So you might meet the hero or villain of your dreams when you venture out the door.