Murphy, Muphry and McKean

Most people have heard of Murphy's Law - Anything that can go wrong, will go wrong. 

This well-known, and oft very accurate, saying has spurned Muphry's Law (don't confuse the two!) which is particular to writers and which states - If you write anything criticizing editing or proofreading, there will be a fault of some kind in what you have written. 

This is another very true statement which is often only realised after you have pressed the Submit button! 

However, not to be outdone, Muphry's Law led the way for McKean's Law where Erin McKean professes that Any correction of the speech or writing of others will contain at least one grammatical, spelling, or typographical error.

I know that this has definitely happened to me. Has it ever happened to you?