We know about the 50 percent divorce rate, the seven-year-itch and the midlife crisis. We know that affairs happen, and that the phrase "for better, for worse" can prove highly subjective over the course of a marriage.

Yet when a long-married couple are divorced, the news often catches us by surprise. Either we suspected nothing or figured they'd made peace with their marital demons.

Recently, several longtime high-profile marriages ended: Minnesota Orchestra conductor Osmo Vänskä and Pirkko Vänskä after 35 years, Fox 9 anchor Jeff Passolt and Lisa Passolt after 29, and actor Mel Gibson and Robyn Gibson after 28 years -- and seven children. Taken together, they cast a klieg light on the humbling question of whether anyone's union ever is safe from harm.

Short answer: It's not.

Longer answer: A vulnerable marriage often has become less about being husband and wife, and more about being mom and dad.

Careful, though; it's foolish to generalize. "The fact is, we have no idea of how much pain people are walking around with," said Rebecca Picard, a divorce mediator in Bloomington.

Yet, she added, "if there's a theme, it's that many times, the focus of marriage does become the children. It's not that they're saying, 'I hope the kids get out of here so I can get a divorce.' Not at all. But the logistics of bringing up kids takes over their lives and is sufficiently interesting that they don't look at other issues."

People also change over time, she said. Older people become less willing to put up with irksome habits. One of them may have a burst of personal growth. "Sometimes, something comes along that gives them a glimpse of a life they could have," Picard said.

When a third party is involved -- the notorious affair -- that provides a visible reason for the divorce, but rarely is the sole factor, Picard said. "Psychologists would say the affair is not the cause, but the symptom of a marriage that's in trouble," she said. Coverage of Mel Gibson's divorce has focused on his young Russian girlfriend, but many stories also describe his wife as "long-suffering," with the couple separated since late 2006, shortly after his infamous profanity-laced DUI arrest.

Susan Zimmerman, a marriage and family therapist in Apple Valley, has noted a gender factor in long-married divorces: Women often are the ones who initiate separation and divorce proceedings. "These aren't awful, abusive marriages; just unsatisfying," Zimmerman said. "They may not even realize that their relationship is in trouble until the kids are gone. Then it's, 'We still have to stay home? We can go out now.'''

As expected, marriages are most susceptible to divorce in the first seven or eight years, according to U.S. Census Bureau statistics. Ten percent of marriages end after five years, and another 10 percent five years later. Then there's a period of stability, with the 30 percent level reached only around the 18th anniversary -- coincidentally enough, a time at which kids begin to leave home.

Zimmerman said that money is the second-most-common cause of marital splintering. "One or both of them have a tolerance break," she said. "They've known that money is a hot-button topic and so have avoided it because they've never found harmony." There may be discovered secrets: a business more leveraged than a spouse knew, or concealed credit-card debt.

Divorce gets very personal very fast, Picard said, but divorce after decades of togetherness can be especially harrowing.

"These divorces are different," she said. "The identity issues that come up are just huge. People are reviewing their entire lives, calling them into question. For the person who didn't want the divorce, the grief is just overwhelming. It goes to the bone marrow. It's not only, 'What do I do?' but, 'Who am I?'"

The task of fending off late-in-life divorce begins right after you hear, "You may now kiss the bride."

"Couples need to learn to speak honestly and not offensively," Zimmerman said. Don't always focus on the present, but talk about the future. "In young marriages, there's an excitement and sexual energy; as you grow older, it's more about being paid attention to, being valued.

"It's easy to get careless or lazy in nurturing the relationships, and the healthiest message you can take from this is that home is not the place to get lazy, but it's where you can get away with it for a while." When trouble arises, don't immediately consider yourself doomed, but realize that you have received a wake-up call.

"Every marriage has issues that are unresolvable," Picard said. "The question is whether you're going to go to the mat over those, or manage them. I haven't seen people giving up on marriage too easily; they really struggle. But people also have to be willing to be willing."

Kim Ode • 612-673-7185