I am constantly editing my writing and silently sitting there reading what I've written to make sure that you, the reader, will enjoy what I've written. It is amazing how many times I can silently edit the same sentence over and over---only to discover that it has an error, either a missing or added word or even worse, a misspelling.
The mind is a complicated mechanism. It can see what is or isn't there, as needed.
Using an example which irks me repeatedly...
A certain insurance company has random people reading a signs that says:
15 minutes can save you 15%.
But, the person reading the sign, always, ALWAYS says...
5 minutes can save you 15% on car insurance.
I've stopped the ad (froze the screen) and carefully checked to make sure I am seeing what they are saying and never once have I ever found those last 3 words. Yes, I realize it is just a commercial, but it proves my point. The reader is giving us more than what is printed and this holds true for almost anything a reader will peruse. Or, in the case of me editing and/or writing.
I did a reading of another author's book at a meeting. I have no idea how many times I'd read the couple of paragraphs making sure I was familiar with the piece so I wouldn't screw up when I stood in public. The moment of truth came and as I read the segment aloud, I stumbled twice on poor sentence structure that my mind had blindly fixed for me within my mental readings. In one place, an extra word was added, the other place, a word had been left out. After the incident, I had a friend read the segment and he said it sounded just fine. I then had him read it aloud. He stumbled at the exact same spots.
I'm sure you've had the email sent to you which has the words misspelled... well, actually, not misspelled, the letters are arranged incorrectly. You raed tihs snetnece wtihuot truolbe. The mind rearranges them to make it sensible to you. The same holds true if a word is missing or added. Your mind fixes it on the fly.
Always make sure what you read is what is written. It can change the whole concept.
Until next I ramble on...