WASHINGTON, D.C. (CNA) - Of the countless Catholic couples who have come through Father T.G. Morrow's office in Washington D.C. for marriage counseling, two remain imprinted in the priest's mind even today.

In many ways, these two Catholic couples were the ideal; they were open to life, they formed their children in the faith and they frequented the sacraments.

But both of these marriages fell apart. The culprit? Anger.

"Anger is a poison," Father Morrow, a moral theologian and author of "Overcoming Sinful Anger" (Sophia Press, 2014) told CNA. "If a husband and a wife are angry with each other a lot, it destroys the relationship. It makes it so painful that people want to get out of that relationship."

Everyone experiences the feeling of anger. It's a natural, uncontrollable response to the behavior of others, he said. And anger can sometimes be righteous - St. Thomas Aquinas once said anger that's aligned with reason is praiseworthy. But most often that natural response of anger morphs into sinful anger, which is motivated by a desire for revenge, the priest noted.

And this sinful anger has a devastating effect on relationships.

"It's extremely important that people realize that (anger) can be a very serious thing, especially if they have major outbursts that really hurt other people," Father Morrow said.

Anger is so destructive that many marriage experts recommend couples have five positive interactions for every negative interaction.  

"This anger, when it's expressed badly, is a poison to every relationship," he said. "Married people need especially to be careful about this...to work on this and to overcome this."

Since the feeling of anger is natural and unavoidable, Father Morrow said it is important to know how to express anger or displeasure in an effective and positive way. The first step: decide if it is worth getting angry.

"People get angry about little, trifling things," he said. "You have to say "Is this worth getting angry about?" If not, then you have to let it go. Just forget it."

If your anger is justified and a confrontation would promote the good of the other, use humor or diplomacy to express your anger. If a confrontation would not promote the good of the other, then Father Morrow suggested offering that anger to God as a sacrifice for your sins and the sins of the world.

"(Anger) won't go away automatically in one try," he explained. "We have to keep giving it to God as a sacrifice."

Father Morrow said this approach to anger does not mean every person should suddenly become a doormat who is too cowardly to express dissatisfaction with the actions of another.  

He used the example of St. Monica, the mother of St. Augustine of Hippo. Many of the men in Tagaste at the time had violent tempers, and St. Monica's husband was no exception. When he would come home and yell at St. Monica, she would stay quiet. Some time after her husband's explosion of anger, St. Monica would approach her husband and calmly address his treatment of her and his complaints.

"She was the furthest thing from a doormat," Father Morrow explained. "She had a specific goal that she wanted to become holy and she wanted to covert her son. She pursued her goals ardently and as a result she converted her violent husband and eventually converted Augustine."

For more information, check out Father Morrow's book "Overcoming Sinful Anger" (Sophia Press, 2014). The 102-page book reads like a manual and draws from Father Morrow's experience as a marriage counselor and spiritual director and his doctorate in Sacred Theology from the Pope John Paul II Institute for Studies on Marriage and Family.