A few more Rules may fitly be given here, for correspondence that has unfortunately become controversial.
One is, don’t repeat yourself. When once you have said your say, fully and clearly, on a certain point, and have failed to convince your friend, drop that subject: to repeat your arguments, all over again, will simply lead to his doing the same; and so you will go on, like a Circulating Decimal. Did you ever know a Circulating Decimal come to an end?Lewis Carroll
(from Eight or Nine Wise Words About Letter Writing)