McKean's Law

Any correction of the speech or writing of others will contain at least one grammatical, spelling, or typographical error.

Skitt's Law

Any post correcting an error in another post will contain at least one error itself.

Muphry's Law

If you write anything criticising editing or proofreading, there will be a fault of some kind in what you have written.

Hartman's Law of Prescriptivist Retaliation

Any article or statement about correct grammar, punctuation, or spelling is bound to contain at least one eror.