Murphy's Law of Accessibility
Refers to the infuriating situation of something you need's usually being at the bottom of a pile, at the back of a drawer/shelf, etc.
I have a 2--vertical-layers-deep stack of plastic totes for storing my DVD-collection, arranged in alphabetical order. It's often the case that the disc I want to watch has a title that is near the end of the alphabet, though, and so I hafta laboriously remove all da rest of da crates to access the very back/bottom box... yep, a classic case of Murphy's Law of Accessibility!