I mean proof is in the pudding! It's amazing how the human brain works. I have just finished writing a draft of a feature script that I would have re-read literally hundreds of times. So it was much to my surprise and consternation that one of my producers emailed me a PAGE of typos. Surely she jests, I thought to myself. I couldn't have missed that many errors... could I?
Indeed I had! Whole words missing in lines of dialogue. Punctuation gone on safari. Experimental spelling and inventive grammar. How is this possible?
I believe the reason is this: I know exactly what every line in the script should be. My brain magically fills in the blanks and compensates for any errors thereby bypassing the evidence before my very eyes.
You may have seen deliberate demonstrations of this where complete sentences are misspelled but as lnog as the first and lsat letter of erevy word is correct the brain will automatically recognise each wrod and comprehend the meaning. In my case, a word missing in a dialogue is easily overlooked. (Yes, I know... line).
One of the reasons script readers cite for looking unfavourably on a script is typos. Always struck me as one of the easiest things to get right and I would agree, makes your work look amateurish. But I would say to you this - it is absolutely VITAL you have fresh eyes look at your screenplay because of the above calibration your brain may be doing without your conscious assent!
Also, after spending hours upon hours on a rewrite, I don't know about you, but I can't see the wood for the trees sometimes. The other factor at work is this: I get caught up in the story. I race along with the drama, the emotion, the action... and forget to slow down and check each damn word. A good sign, granted... but not if meticulous examination is required.
So make sure someone else proof reads your script! You'll be surprised what they might find.