Most authors are surprised to find out the hardest part of the publishing process is not writing the book. Want to know the hardest part? It's the final proofing. Getting a book completely cleaned up and error-free is no small job. In my opinion, it is absolutely the hardest part of the job. What people generally don't understand is that there are several editorial roles on most publications. Authors generally have no idea the differences in those roles -- and the proofer has the hardest job of all. To help you understand the editing process, here are the roles you commonly see (and if you look on magazine mastheads you'll see these roles broken down):
Editor in Chief -- this person decides the broad content and takes a more global role on the publication. He or she manages the scope and reach of the publication. When you see the specific stories in the publication, the editor in chief probably didn't decide on the specific stories as much as he/she approved and watched over management of the issue. In the book world, the editor in chief would approve the book being accepted at all and ensure the overall quality is acceptable. The editor in chief stays out of the weeds.
Managing Editor -- this role holds the business process. The managing editor typically assigns and maintains the relationship with the staff. You will not see a managing editor do much hands-on editing. He/she will manage schedules, production deadlines and people. The back-end business processes typically are the responsibility of the managing editor.
Editor -- the average editor gets into the weeds of the stories. He/she will be actively involved in making sure stories or books are well-written, organized and make sense. The editor will get in and revise content and clean up weaknesses.
Copy Editor aka proof reader -- this is the one with that hard job. Final grammar and spelling checks go through this person. The copy editor is often a fact checker too.
Those critical readers aka the grammar police (my name for those picky individuals that for one reason or another decide to make it their jobs to police our books) will be hard on authors when they find mistakes. I always become very annoyed with the grammar police and would challenge the "officers" to show a little more understanding when we're dealing with (on average) 50,000 individual words in a single document. Imagine the challenge of getting 50,000 words absolutely right each and every time. Until you've had that responsibility, I would caution you to throw "stones". We certainly do our utter best to ensure our manuscripts are as clean as possible, but every now and again, we show our "humanity" and miss one in 49,999 words. If you feel morally superior because you happen to find one of those mistakes then let me see you do proof a 50,000 word book! Perfectly!!! And for the record, I see mistakes in books published by the big corporate machines all of the time.