The other night I heard a student telling another how she had avoided a proofreading calamity. During class that night, each student had to get up and argue in support of a motion they had previously turned in. The student realized that she had inadvertently left out the word "not," so she covered her error by arguing the other side of the case. Of course, in the real world, you can't just switch sides.
The student's story reminded me of an unemployment case I attended years ago. The woman seeking unemployment benefits was a law student who had been fired for incompetence by her law-firm employer. Although several errors were given as grounds for her firing, the beginning of the firm's lack of confidence in her abilities stemmed from a near-perfect memo she had prepared. Howevere, she had left out the word "not" in the subject line of the memo. Although the remainder of the memo correctly stated the law, the most prominent sentence was wrong because of one little word.
The difficulty of proofreading is that when you try to proofread something on which you have been working for a long time, you sometimes see what you meant to write, instead of what you did write, so you can miss important errors. I try to avoid this problem by not working on the project for a day or two before my final proofreading. Some people proofread in a different font or font size than they have used while writing. Others find that printing the document forproofreading, instead of reading it on the screen, does the trick.
Eric Waltmire recently posted his tip for How to Proofread Perfectly. Eric recommends having your computer read the document to you while you read along. See Eric Waltmire's Blog for details. (Eric is an SIU Law alum.)