A list of things to be done or verified, marked off as each is met. It defends against forgetting rather than against ignorance.
Compound of check (Persian shah) and list (Old English liste, a border, an edging strip of cloth; the enumeration sense grew because lists were written on strips of paper); a checklist defends against forgetting a step, not against not knowing one.
It assumes the knowing and guards only the remembering — a checklist cannot tell anyone what to do, only remind them that the doing was already decided, which is why it fails silently against a step nobody knew belonged there in the first place.