Originally derived from https://en.wikipedia.org/wiki/ADM-3A#ADM-3A, which I only learned (maybe from HN) long after becoming a vi user.

Edit: I've wondered whether the Dance Dance Revolution on-screen arrow order https://en.wikipedia.org/wiki/Dance_Dance_Revolution#/media/..., which I also have deep in my muscle memory, is somehow also related to the hjkl arrows (as it also goes ← ↓ ↑ → horizontally).