I don’t know if it counts as a Law, an Axiom, a Maxim, or any other sort of anything — nor do I know if someone has formulated it before (this is one way of finding out). However, in case no one has, I herewith promulgate the following predictable correlation:
The longer you possess a bag (backpack, brief a, satchel, purse, messenger pack), the heavier it gets. This holds even after the bag has been emptied of detritus and refilled with things you really need for your day.
I observe this, you will not be surprised to know, because the case I’ve been carrying to and from work, which contains only my iPad, a notebook/holder, my diary (= ‘calendar’ for the benefit of my friends in the States), and a couple other things that have fallen in there over the years, has become distinctly heavier recently.
I suspect, although I cannot prove at my current level of funding, that carrying devices function as Higgs Boson attractors. CERN could probably have saved a lot of time if they’d experimented with physicists’ backpacks and purses. Anyway, there’s AKMA’s Axiom for you.