Oh my good god! This is some debate. Well I will wade in and all I know, or what I have learnt in watching others R's and certainly in my own... lack of communication is the root of all evil. Or the wrong type of communication (90% of arguments are all just noise, nobody listens once you start yelling). So.. if you dont understand your womans mood, ask her whats wrong and listen to the answer. If you think you may be being too controlling and ignoring your H's needs, ask him his opinion and take it on board. So... better listening skills ?
I'll jump in too! I think a lack of compassion is the root of all evil in relationships. Failure of compassion is the primary cause of anger, resentment, contempt, disgust, and abuse in relationships. I speak from my own personal experience.
And I'll add that you have to have compassion for yourself as well as compassion for others.
"Always go straight forward, and if you meet the devil, cut him in two and go between the pieces." - William Sturgis, clipper ship captain, 1830's.