Here's the thing about relationships.

Sometimes they're candlelit date nights, and walks through grassy meadows, and feeding each other cake at your wedding.

But sometimes they're doing the dishes, and comforting a screaming baby, and fighting over whose turn it is to do the dishes or comfort the screaming baby.

Which is to say, while sometimes your love and passion for each other is obvious, sometimes it's really, really not.

So how do you know if your relationship is terrific -- or heading south?

Psychologists have spent years studying the traits that are fundamental to successful long-term relationships and come up with a few key ideas. We rounded up some of their most surprising insights below.

A word of caution: If you notice that your relationship doesn't meet all these criteria, that does not necessarily mean you should end things with your partner. Consider this list a general set of guidelines that can help you start evaluating whether your current relationship is bringing you satisfaction and happiness.

You think about your partner often when you're not together

In 2007, researchers randomly dialed nearly 300 married people and asked them a series of questions about their relationships, as well as how in love they felt.

Results showed that certain relationship characteristics were linked to stronger feelings of love. One especially interesting finding: The more often people reported thinking about their partner when they were apart, the more in love they felt.

The same study included a follow-up experiment with nearly 400 married New Yorkers, which found that difficulty concentrating on other things while you're thinking about your partner is also linked to strong feelings of love -- especially for men.

You respond positively to each other's good news

Business Insider's Lauren Friedman has reported that one litmus test of a happy relationship is how enthusiastically each partner responds to the other's good news.

A Psychology Today blog post breaks down four ways a man could respond after his wife tells him she got a promotion at work:

An active-constructive response from him would be enthusiastic support: "That's great, honey! I knew you could do it, you've been working so hard."

A passive-constructive response would be understated support -- a warm smile and a simple "That's good news."

An active-destructive response would be a statement that demeaned the event: "Does this mean you are going to be gone working even longer hours now? Are you sure you can handle it?"

Finally, a passive-destructive response would virtually ignore the good news: "Oh, really? Well you won't believe what happened to me on the drive home today!"

Perhaps unsurprisingly, the response that's most closely linked to relationship satisfaction is the "active-constructive" response.

You spend some time apart, with your own friends

Over the past few decades, we've started placing increasing demands on our spouses. As Business Insider's Jessica Orwig has reported, no longer do we expect them to be financial partners, protectors, and companions -- now we also want them to provide personal fulfillment.

The psychologist who produced some of these findings, Eli Finkel, suggests that if you want to be happy in your marriage, it's best not to look to your partner for all your existential needs. Finkel recommends finding yourself in hobbies, friends, and work as well.

You have a similar sense of humor

Neil Clark Warren, psychologist and founder of dating site eHarmony, previously told Business Insider that humor can be a "social lubricant" in a romantic relationship.

Meanwhile, Business Insider's Erin Brodwin has reported that having a "private" language with your partner -- i.e. nicknames and jokes that no one else would get -- can help facilitate bonding and often predicts relationship satisfaction.

You split chores evenly

In one poll, as many as 62% of adults said that sharing chores is very important to a successful marriage. Interestingly, given societal stereotypes, there was no difference between men and women.

But while men are doing more housework than they were in years past, research has found that women still pick up most of the slack.

You try new things together

For a study published in 1993, researchers looked at the relationship quality of more than 50 middle-aged married couples and assigned them to one of three groups.

One group picked new and exciting activities to do together for 90 minutes a week -- like going to a play or dancing. Another group spent 90 minutes a week doing pleasant but routine activities together -- like going to the movies. The last group wasn't asked to change anything.

After 10 weeks, the researchers re-assessed the couples' relationship quality and found that those who had tried new and exciting undertakings were the most satisfied.

As The New York Times reported in 2008:

Dr. Aron [one of the researchers behind the study] cautions that novelty alone is probably not enough to save a marriage in crisis. But for couples who have a reasonably good but slightly dull relationship, novelty may help reignite old sparks.

You don't have a lot of extreme downturns in your relationship

Researchers recently looked at nearly 400 dating couples and used their feedback about their relationships to identify four different patterns of commitment: dramatic, conflict-ridden, socially-involved, and partner-focused.

As psychologist and relationships expert Gary Lewandowski explains on Science of Relationships, dramatic couples showed a lot of fluctuation in their commitment to their partner over time.

Partner-focused couples saw their partners positively and mostly experienced fluctuations in commitment when they couldn't spend as much time together.

Socially-involved couples usually experienced fluctuations when their friends and family changed what they thought of the relationship.

Finally, conflict-ridden couples fought often and had a lot of mini-fluctuations in their level of commitment.

As it turns out, partner-focused couples were most likely to get more serious in their relationship, and dramatic couples were most likely to break up.

You know how to recover from a fight

Psychologist and relationship expert John Gottman previously told Business Insider that the No. 1 shared trait among successful relationships is being able to repair the bond after a fight.

It's not about not having conflict at all -- instead, it's about the way you approach it. Gottman told Business Insider:

"The thing that all really good marriages and love relationships have in common is that they communicate to their partner a model that when you're upset, I listen.

"The world stops, and I listen. And we repair things. We don't let things go. We don't leave one another in pain. We talk about it, and we repair."

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