Play nice?

I don’t understand how two people who want their relationship to work find it so difficult to be nice to one another. What part of “treat your partner with love and respect this week” would lead you to believe that swearing and put-downs could work? I know it’s hard to “play nice” when your partner has had a bad day and is not meeting your expectations, but swearing…really? How old are you? Do you want your marriage to work or not? Is it that hard to treat the person you love with some semblance of understanding and love? I know the answer …. sometimes… is yes. But when your marriage literally depends upon it? Come on. Do you think you could be nice for a week if you absolutely had to be nice in order to stay together? Thoughts?