Why does `nnoremap K ko` not work on first line

Question

Run vim --clean, :nnoremap K ko, and press K -> Nothing happens.

Run vim --clean and press ko -> Vim enters insert mode on second line.

Why?

(I know about big-O, this is just out of curiousity, it appeared in debugging a more complicated map)

Answer 1

This happens, because a macro usually aborts, if not all of the typed keys work. In your case, the k in the first line is an error, so the macro won't try to run the o command.