"Muphry's Law is the editorial application of the better-known Murphy's Law. Muphry's Law dictates that (a) if you write anything criticizing editing or proofreading, there will be a fault of some kind in what you have written; (b) if an author thanks you in a book for your editing or proofreading, there will be mistakes in the book; (c) the stronger the sentiment expressed in (a) and (b), the greater the fault; (d) any book devoted to editing or style will be internally inconsistent."
So what's an example? From the same site:
"In The Complete Guide to Editorial Freelancing (Dodd, Mead & Co., New York, 1974) Carol O'Neill and Avima Ruder acknowledge the assistance of 160 editors and friends, which is very generous of them.
Or could it have been a marketing ploy? (We should sell at least 160 copies of this one, Mr Dodd. I am sure you are right, Mr Mead.)
It's a fairly useful sort of book, worth the fifty cents I paid for it some years ago, but I have trouble getting past page 38. On this page the authors remind us that "Country names change, and a book that uses an old-hat appellation will seem dated"... They then tell you where to look for up-to-date place names and give a few examples of countries recently renamed, among them Cambodia, now "Sri Landa"."