One of the first things you learn after you get married is what hard work it can be. All those quirks that were so endearing when you first met are now grounds for murder. (The loud chip crunching! Has he no decency?) Add a few years under your belt and you realize that there are almost more ways to screw it up than to keep it together. Don't throw in the towel just yet — these unbreakable rules will keep you both in check.