Think about how you typically approach a conversation on a personal, high stakes topic. It could be with your mother-in-law over how you raise your children; your boss when you think you have been unfairly treated; or with a friend you feel has behaved inconsiderately. While you may, in theory, accept that people see things differently, deep down, who do you think is causing the problem? Why, they are of course!
 
When you step into a conversation convinced you are right, that you own the moral high ground and that if the other person would just see it your way, there wouldn't even be a problem, you're not going to get very far. There's no real conversation. At best, you tell the other person how you see the issue, you tell them how strongly you feel about it, and then you tell them what you want them to do about it. You think you have agreement? Unlikely! Is there commitment? Hardly! Worst of all, it doesn't solve the problem. So you broach the subject again, only this time you explain the problem more forcibly, you say more strongly how you feel, and you threaten dire consequences if they don't do something about it.
 
One of the hardest parts in preparing for a conversation on a subject about which you feel strongly, is to accept that since you are part of the relationship, then you are part of the problem. It may simply be that you have not spoken up about how you feel and have given the other person no way of knowing that you are unhappy, and therefore no reason to change their behaviour. It may also be that their view of the situation has just as much legitimacy as yours. It might even be that you are plain wrong!