Relationships aren’t easy, that’s for sure. While there isn’t a secret sauce for guaranteed relationship success, there are some relationships that never work and are more likely to fail than others.

There are quite a few reasons why this particular relationship is so destined to fail, making it a poor choice if you’re looking for stability with a partner. To those looking to find a partner, use this information to guide your decision; consider it the best relationship advice you'll get. And for those who are already shaken up, use this info to make some serious evaluations.

How much does an age gap matter in a relationship? This is the biggest indicator of a relationship that is doomed to fail, says a 13-year study from the University of Colorado Boulder.

According to the study, couples with large age gaps are less satisfied in their marriage. 

Research on thousands of Australian households shows that couples who are closer in age tend to be more in tune with what their partner wants out of life. Things like children, spending habits, and overcoming economic decline are much better handled by couples who are closer in age.

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Not surprisingly, out of the people surveyed, it was the men who had younger wives who were the happiest, and men who were married to older women tended to be the least satisfied.

"If there is too much of an age gap you run the risk of both of you wanting different things in life," says dating expert James Preece. "One might want to travel while the other has already done that, for example. Maturity levels can vary dramatically and arguments about jealousy and money can be common," he told The Independent.

Couples in relationships need to want to have the same future together for them to work. Another study conducted by Utah State University found that individuals with two commonly shared values had higher marital satisfaction than those without closely shared values.

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Researchers were quite surprised to find that women who were married to older men were the most unhappy, while those married to younger men were more satisfied. 

It seems that in the case of both genders, a younger partner is preferable. However, those that were the closest in age were the happiest.

“If you look at marriages over time, the people who are married to a much older or younger spouse tend to have larger declines in marital satisfaction compared to spouses who are similar in age,” McKinnish explained in a Boulder University podcast. For the relationships that never work, it turns out that the closer in age you are, the better. So, cougars, you might want to think twice.

Shannon Ullman is a writer who focuses on travel and adventure, women's health, pop culture, and relationships. Her work has appeared in the Huffington Post, MSN, and Matador Network.