It has happened twice now, toward the end of the final draft of a project. There it is, a glaring typo discovered at the beginning of the story. A typo that has been there all along––or at least for several drafts––but completely overlooked.
We were very close to finalizing the galleys of The Confessions of Adam when it was discovered, in the first chapter, instead of referencing the trunk of a landmark tree, there was referenced a tree truck.
And once again, just a few weeks ago, a beta reader, at this late stage in my current project, found––in the preface–– that the word first had been written as fist.
The point here is you must engage beta readers and editors. Both of these were found by such collaborators. Neither was found by me, my publisher or my agent. And in the case of Confessions, most had poured over the manuscript, some of us many, many times.
Being the author, you will become utterly blind to such errors. Your brain will determine what is on the page instead of your eyes. Your only hope is collaboration with others before your manuscript is out in the wild and such mistakes are found by readers. For readers miss nothing.