I can't proofread because my brain corrects mistakes. So omitted words are filled in, spelling is corrected, and more egregious errors effectively sanitized before my mind lets them in. Basically my brain sees what it wants to see, not what is written in front of my eyes.
Unfortunately, this same process of semasiological sanitation happens for my own words.
I'd be the world's worse proofreader which probably explains my very short* tenure in the sub-basement of sub-editorship (I was good at headlines and captions though).
The only vague solution I have for this problem is to make the computer read things back to me, for some reason the process doesn't impact the text when spoken.
There's probably a medical definition for this. I figure that at this point everyone is the first world is either 'gluten intolerant', 'a bit dyslexic' or 'somewhere on the autistic spectrum.' I demand my own distinct pathology.
*see, edited to add this, this word was totally omitted the first time, but my brain wrote it.