>,>I used to teach IT (WP, S/S, DTP, Access) to secretarial students. Once I was invigilating a Pitmans WP exam and, at a cursory passing glance, I could spot at least 3 errors on 1 student's paper. She and a friend finished before time and asked if they could leave. Now I wasn't supposed to give any feedback but we were on a friendly basis. I settled for "you may, of course, but if I were you I'd use the time to check my papers". They both did and later thankfully informed me that they'd spotted umpteen errors besides those I'd spotted.
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>>I was used to marking their mock exams and spotting all the errors (i liked to think) without the answer book.
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>>Yet I can't properly proof-read a single SQL statement of my own when I know what I'm looking for!
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>It's a common problem and happens to me all the time. I think that, because you know what is supposed to be there, the mind sees what is supposed to be there if it is at all close -- without actually processing the data.

If a stage illusionist can truthfully say to his whole audience, "... and none of you saw the man dressed in a gorilla suit come on and take the banana" then we can miss the odd comma :-)