What do couples fight about most? Money (what to do with it and why there’s not more of it), sex (how much to have it), time (how to spend it) and family (why your parents drive me crazy and why my parents seem to drive you crazy) often top the list.When you put all these wonderful dynamics in a holiday stew, it’s a recipe for disaster. With so much to figure out—travel, gifts, planning various events—it’s no wonder many couples get stuck and stuck again thinking about where to go and what to do for the holidays.If you’re not fighting with your partner about which parties to go to, then it’s which set of in-laws to see for Thanksgiving, or where to go over Christmas (or your holiday of choice) and New Year’s. In fact, there’s pretty good reason to think the questions Where should we go and who should we spend the holidays with? represent a perfect storm for an argument with your partner.There are many painful permutations of how these issues can combine to cause a fight or disagreement. I’d like to go into detail on two important aspects that are key to relationship harmony: equity and tolerance.Equity: Our Brains are Wired for FairnessWhat does it mean to say our brains our wired for fairness, and what the heck does this have to do with a fight about where my husband and I should spend New Year’s? In his new book, “Social: Why Our Brains Are Wired to Connect,” the psychologist and neuroscientist Matthew Lieberman argues that because cooperation activates the brain’s basic reward systems (for example, see this excellent article), behaviors that are equitable and fair are social rewards.MORE: When to Walk Away From a FightLieberman also argues that these social rewards are critical to our survival and that fairness within a relationship is a sign of social connection. When we perceive our partner’s request to “see my parents for Thanksgiving, then have a quiet Christmas at home” as inequitable, it immediately signals a gap in our relationship.For example, your reaction might be: “Wait, you want to just see your family this year? That’s what we did last year, and it would be unfair to me and my parents to do that again. Why does everything have to be about your mom and what her needs are? You are such a momma’s boy!”Yikes, this doesn’t sound too good.When it comes to the holidays, though, determining what is fair can indeed get tough. His parents live by you so you actually seem them quite often; your parents are far away and the visits are more seldom, and limited to major holidays and birthdays. Now your husband is upset because his parents never get to spend Thanksgiving with the grandkids. You don’t think it’s fair to have to stay in town when you see his parents every other weekend. On top of all this, you have your mother breathing down your neck—she hasn’t seen you in eight months and would really like a visit.The best advice I can give on this topic is to go for equity in order to find balance. Show your partner that you’re willing to compromise, but do not do so at the expense of your own needs or desires. Be open, be direct and go for solutions that are win-win. Think about long-term equity, not short-term gains; that is, even if you give up a few holidays in the short-term, it’s possible to get them back in the long-term.QUIZ: What’s Your Relationship Style?As you do this, don’t throw your partner under the bus. Statements like this are no good: “I really want to be there mom, but John insists we see his family this year.” Instead, simply state how hard it is to find a good balance: “I really want to be there mom, but we have to keep things fair in the family, and we’ve decided to go to John’s parents this year, then come to you guys next year. I am sorry—I wish it was easier.”Tolerance: Sometimes You Gotta Suck It UpThe entire fairness scheme I described above can fall apart if you can’t tolerate his family (or vice versa). “Yes, honey, it’s true that it would be fair to go to your mom’s for the holiday. But, she’s such a raging narcissist that it would be cruel and unfair to force me to spend another stinking holiday with her. Also, do you really know how much she drinks?”So many fights about in-laws and family have to do with tolerating someone in your partner’s family. Or tolerating the boredom of being with your partner’s family. Or tolerating being out of your exercise routine and being forced to go vegetarian for a week. Or tolerating being stuffed in the guest room for a week next to a litter box when you have cat allergies. (These are not personal experiences, by the way.)These situations challenge our patience beyond belief. It may also be the case that everyone sympathizes with you and knows his mom is a narcissist, but it’s just the kind of thing everyone has learned to tolerate…and so will you in time. Alternatively, you’re the problem. Everyone seems to get along with his mom just fine, but you don’t.Whatever the case, the best thing to do is to think about this situation from your partner’s perspective. If I were in his shoes, how would he want me to act? The answer is so easy: Just suck it up, try to be nice, try to have some fun, try to relax and please stop getting so upset by every little detail.This doesn’t mean you have to love every second of being with your husband’s family, nor does it mean that you cannot ask for large amounts of time for yourself, but it means you need to participate and try to be nice, no matter how you feel. You need to contain your suffering for the sake of the relationship.By participating even when you don’t want to or tolerating an in-law that drives you totally nuts, you’re giving back to your relationship in spades. In this way, you’re also building equity in your relationship and your partner will love you for your great efforts.MORE: Stop Being Too Nice