They decided to do a private experiment on themselves. They would cut out all negativity in their relationship. This doesn't sound that hard. That is, until you consider that negativity in a marriage is, as Hendrix says, "anything you say or do that your partner experiences as a putdown." So, that could be a joke ("It's back again, the attack of the killer perm!") or a criticism ("Honey, I love you, but you're not the most challenging Monopoly player") or a guilt trip ("If you don't really love your kids enough to go to the pot luck, then...") or an outright attack ("You're such a know-it-all!") or even a dismissive look. "We went cold-turkey," says Hendrix. "For a few months, we had very little to say to each other. We couldn't talk. Which let us know how much negativity had been seeping into our lives."

Once they got the hang of speaking and acting differently, the results were astonishing. Their marriage had rebounded. They were happier. The idea of divorce was over. They took the no-negativity approach into their workshops and therapy sessions and got the same result. People recommitted to each other—and found a new kind of joy about being together. This wasn't totally surprising. Traditional Imago therapy teaches couples how to resolve problems by using a specific line of dialogue that reduces stress, anxiety and aggression. "When a couple follows our steps," says Hunt, "they learn over time how to speak to each without negativity. All we did was start at the end." Which, in effect, turned their well-known method on its head. Rather than learning to communicate and thus becoming non-negative to one another, a couple just cuts out the negativity—and then learns to communicate—which for many struggling people is faster and more effective than the original technique.

A decade later, the advantages of the approach are just coming to light in terms of science. "Negativity erodes a feeling of safety in a marriage," says Hendrix. "Neuroscience now shows that when you or your partner don't feel safe, they get anxious, and neither of their brains can problem-solve. So they can't find solutions to arguments."

Like so many seemingly simple things, however, the process is trickier than it seems. People can't click their heels and whisper, "We will not be negative. We will not be negative. We will not be negative." You do have to say this. It's the first step. But what comes next? Here are a few doable ways that Hendrix and Hunt were able to banish negativity and start over—for real.

1. Define the ouch.

The big problem with negativity is that we often don't know that we're engaging in it. Our judgment is clouded about what we're really saying to our partners. "In my case," says Hunt, "I prided myself on all the constructive ways I helped Harville live his life. I had ideas about how he could improve how he dressed. If he said something during a speech that wasn't quite clear, I pulled him aside and told him how he could do it better. I thought I was being his best friend." Hendrix also thought he was helping. He let Hunt know every time she was being too loud or too intense. He was "correcting her" with love.

To remove the negativity, each of them had to admit when the other had unintentionally hurt them. And this is where it takes courage. Because "the one who flinches," says Hendrix, "has to take the responsibility of telling their partner. And it can be scary when you're not getting along." But what's even scarier, when you think about it, is getting hurt over and over—until you give up or leave.

Next: Three more steps to end negativity in your relationship