Because you may find yourself having a dream about having these people in your house and even though its a dream, you will feel obligated to be a polite and gracious host.  But then you will spend all your energy trying to wake yourself up so you can stop this nightmare, only to discover that you may have clicked on too many pictures because now you are back asleep but these people have never left your house.  They have just been patiently waiting until you go BACK to sleep to once again bore you with idle conversation.  This seems to go on for hours, with you waking up to stop the horror and going back to sleep and finding the bigger horror.  I hate you people for leading me down the path of a sleepless night.  Like pregnancy isn't difficult enough.