McNulty writes in the paper, published Thursday in the journal Science, that “even though people may be unwilling or unable to recognize any deep-seated discontent they have toward their partners, that discontent may nonetheless shape their relationship outcomes.”

For the study, 135 newlywed couples from eastern Tennessee were first asked directly to rate their attitude toward their partner; they were then given a test to measure their unconscious, or implicit, attitudes. Researchers showed the volunteers a photo of their partner, and then asked them whether a series of words were positive or negative. The words were things like “awesome,” or “awful” — easily identified as good or bad — and the participants were timed on how long it took them to say whether the word was positive or negative. The couples came back and answered these questions every six months for four years.

Some of the people took longer to identify a word like “awesome” as positive — and as the years went by, those people started telling the researchers they were less and less happy in their relationships. Others took more time to say that a word like “awful” was negative, and those people were generally happier with their partners.