In the first book we wrote we added a preface to the beginning of the book. The book was about Father Time and Mother Nature. They were standing on a cliff together overlooking the ocean and reflecting on the job that God had given them to do. They were discussing the different tasks He had assigned them and that to be able to accomplish these tasks God had given them immorality. We had used the wrong word, it was supposed to be immortality but instead it was immorality, we had forgotten the "t".
It wasn't until after the book was published and my husband was starting to read the book that it came to anyone's attention. It had slipped through the computer's spell check program and no one had caught the mistake, not even our proof-reader.
The human element is important because the computer will not catch everything because if the word is spelled correctly, it will skip over the word. Unfortunately, the human element isn't flawless either, but it is something to remember when you do finish your work, have more than one person review it for typos. Hopefully if more than one person reviewed your work then it is probable that the mistakes will be caught before you go to print.