Here it is, personally witnessed enough times now that I have promoted it from simple theory to law:
If you order something to be delivered to your house on your work-at-home day, it will be delivered a day late, you will be at work, and you will get stuck in the loop of multiple delivery attempts. The carrier will max out on re-delivery attempts before your next work-at-home day, and you will be hauling yourself down to a distribution center on the edge of town to pick up your package. If you order something to be delivered to your workplace on a day you will be there, it will be delivered to your workplace on your work-at-home day.
(I’m working in Berkeley today and the big monitor I ordered to make myself more productive is sitting at Yahoo! HQ, delivered a day earlier than expected. Sigh.)