After 35 years of marriage, Mark Earnhart came home one day and told his wife, Jeanine, that he wanted a separation. He said he was tired of the bickering and tension, the lack of communication, how they never did anything together anymore.

His wife sadly agreed that the marriage seemed broken. So Mr. Earnhart, a chiropractor, moved out of their home to a furnished apartment on the other side of San Juan Island, in Washington.

Three months later husband and wife were back together. They have been married now for 42 years.

It seems counterintuitive: How can a separation save a marriage? When a couple splits—even for a trial period—isn't that just a pit stop on the way to divorce?

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