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At some point in my mid-thirties, it started happening to young couples around me. Their relationships began fracturing and falling apart, and it wasn't always the people you would expect.

These were good folks with good intentions who said every word of their marital vows with conviction. But various circumstances and choices began pressing upon them, and eventually, I saw them go through extreme stress, separation, and sometimes, divorce.

I don't think there's a magic formula for ruining your marriage, but based on my observations over the last few years, there are a few easy ways to turbocharge its demise. Here are five of them:

1. Intimate, opposite-sex friendships. We recognize the danger of getting into a physical relationship with someone else, but we often forget that it's just as dangerous for us to become emotionally close with someone of the opposite sex. It usually starts innocently enough — a friend at work asks you for advice, treats you to lunch, or confides in you behind closed doors. Over time, those kinds of interactions can be a gateway to emotional intimacy, and with the right combination of stress, attraction, and marital frustration, that friendship can easily turn into something more.

2. Constant criticism. We all deal with enough guilt and shame to keep us feeling down. When the person who knows us best reaffirms our shame with constant criticism, it can become too much to bear and make us want to distance ourselves from him or her.

3. Hypersensitivity. Our spouse is going to point out things about us that we don't want to hear. Joseph Pulitzer once said that those who are startled by unflattering facts should "blame the [person] before the mirror, not the mirror.” A spouse who is hypersensitive won't be able to listen the ways he or she needs to change, and as a result, fixable problems will persist and create resentment in the marriage.

4. Unrestrained in-laws. You may be used to dealing with your family, but your spouse doesn't have nearly as much expertise. You've got to listen when your spouse says your family has weird dynamics and take your spouse's observations seriously. You've also got to step in and set good boundaries, especially if your family turns their dysfunction on your spouse. When spouses fail to do that, it introduces all kinds of unnecessary triangulation, tension, and feelings of betrayal into the relationship.

5. Isolation. If your marriage is struggling, you can doom it by keeping all the struggles behind closed doors and refusing to reach out to a counselor who can help you work through your issues. Married couples tell themselves they can fix it over time. But by the time they realize how incapable they are at untangling all the knots of dysfunction, it's usually too late.

Anyone who has been married could add more bullet points to this list. But just as important as the ways we can undermine our marriages are the many other ways we can reinforce them. That involves doing things like intentionally building friendship with our spouses; offering regular praise and encouragement; acknowledging our spouses' criticisms and choosing to change; keeping healthy boundaries with third parties; and, if necessary, doing a martial checkup with a therapist or pastor every once in a while.

It takes a lot of work to keep our marriages healthy, for sure. But a good marriage is the gift that keeps on giving, even if it's just building our character, which is what makes all the hard work worth it.