My father in law still worked with lead printing blocks that had to be mannualy set on the plate. Novices on the task would have their work checked; seasoned workers developed the hability to read text backwards. There were typos and mistakes, obviously, but not as many as one would expect.

I proof read my own writings as well but it comes a point where a fresh set of eyes is highly advisable to find those little quirks and easily overlooked mistakes. If publishers can't be bothered to check their author's work, something is very wrong. An author self publishing doing some mistakes is forgiveable but publishers spent to much time and resources making themselves the only "professional and legitimate way" to be published to enjoy the same leniency.