[mont]

It's probably set up like that to mirror vim bindings, after all, "J" does look __sort of__ like a down arrow.

[atoav]

I always remember it as “jump” and “climb”. Climb doesn’t start with k, but fair enough.

[majewsky]

When I learned HJKL, I used the following mnemonic: The J key (like the F key) has a little bump at the bottom to indicate the resting position for the index fingers in 10-finger writing. Since the bump is at the lower edge of the J key, that means that J goes down.