When people are in emotional pain, they tend to speak and act in ways that sound angry and aggressive. And if you, too, are in emotional pain, you are likely to speak to the other person in ways that he will perceive as angry and aggressive. Each person adds to the emotional pain of the other, and the distress of everyone involved keeps increasing.
When you are calm, it's easier to see the emotional pain of others. That is when you can build up your attribute of compassion. The goal is to have so much compassion that even when you personally are experiencing emotional pain, you are able to be sensitive to the emotional pain of the person with whom you are interacting.
Coming from a place of compassion you will be able to address the thoughts and feelings of the other person in a way that alleviates his distress. Then he is more likely to speak and act more sensibly and reasonably towards you.
(from Rabbi Zelig Pliskin's book: Harmony with Others, p.130, artscroll.com)