A black box originally meant a coffin. A light box was a bed for waking up in or a garden full of unmarked snow. The black box would be opened & its contents subjected to ritual examination — a kind of haruspicy to divine the past. We would stand around making small talk in the presence of the dead & see what made their eyelids twitch. The light box couldn’t be opened because on closer inspection, it turned out to include everything. To examine its contents, you started with yourself.
Thanks to John Miedema and Rachel Rawlins for the inspiration.