Editing your own book is nigh unto impossible. It’s all about left brain language translation of right brain creativity. Your idea generates in your right brain as an entire entity, full-blown and in full color, all its dimensions intact. But when the right brain passes this idea on to be interpreted into language, much of it does not translate and is left behind.
For the reader, at least. But not you. The idea is still intact in your right brain. Consequently, when you read your own work your brain fills in any gaps that may have been left. You get it! Even if your reader doesn’t.
And so we enlist other editors to assist us. That is good. It helps a lot. But everyone suffers from the tendency to fill gaps. As a consequence, the last errors to be corrected in your manuscript are omitted words and repeated words.
But why is is this so? It is is because everyone forms images in their right brain of the picture you are drawing. Everyone is familiar with certain word word patterns. Therefore, when you omit word that your reader expects will appear, this omission may well be missed or an additional word not noticed not. Our brains simply fill in gap.
So the last thing you or your editor should do before pushing the publish button is read through your manuscript one one last time looking specifically those omissions and repeats. Or th brn wll fll it in!