Black Friday's retail sales numbers looked good, so why are stocks slumping today? The headline figure, showing a healthy increase over last year's numbers, looked great. However, the devil is in the details, and they show some rather dour internals. It isn't my purpose to review them here (too busy trading), but many shoppers indicated in surveys that they have alread completed all their holiday shopping. (I am one of those. I finished shopping more than a week ago. However, I've always tried to complete my Christmas shopping list before Thanksgiving.) Furthermore, retailers have slashed their prices so far already that margins are terrible.