Muphry’s Law dictates that:

1. if you write anything criticising editing or proofreading, there will be a fault in what you have written;
2. if an author thanks you in a book for your editing or proofreading, there will be mistakes in the book;
3. the stronger the sentiment in (a) and (b), the greater the fault; and
4. any book devoted to editing or style will be internally inconsistent.

Muphry’s Law also dictates that, if a mistake is as plain as the nose on your face, everyone can see it but you.