I feel (OK, felt your pain, OK, maybe not quite as bad) when
I did a similar thing. The same old same old, working tired
and the next thing I knew I had a 7/8" narrow crown staple
where it shouldn't be.
Funny thing was, my first thought was, "Damn! That one
didn't set". As I reached for the nail set it dawned on me.
As I said, working tired.
UA100, who has "teknikally" only hurt(1) himself twice in
the shop, touch wood...
(1) Nasty drawing of blood.