Have you ever worked for, been on a team with, listed property for, negotiated a purchase for, or been married to someone who personally could never do wrong and always blamed you (and others) for any error or mis-step? Personally, I like to think of those folks as contra-role models. I never want to be like them. I make a lot of mistakes, and I do my best to learn from each one.
The January, 2009 Reader's Digest listed a memorable quote from General David Clark which puts a little geometry into dealing with others (and this translates into both sales and customer service): "When something goes off-track in your organization, immediately start searching for the source of the problem, in increasingly larger concentric circles, beginning at your own two feet."