Not Murphy’s. Muphry’s.
From Threepenny Planet:
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.
LOL I’m not sure about (b)-(d), but (a) is a classic truth that seems to be finding its heyday in the era of blogging.
Here’s a cute example from today’s AskMefi, in which the questioner asks readers to settle a spousal punctuation bet and manages to include a grammar error and a typo (click to enlarge):
Here’s Muphry at work in Freakonomics, and the apology. LOL BTW in the comments in the second article I learned that when someone incorrectly corrects something that isn’t wrong, it’s an incorrection.