Here are four theories as to why our families drive us nuts, and it would be nice of you to pay attention for once in your life:

The Narcissism of Small Differences

Sigmund Freud noted that people who lived near each other and were ethnically similar—“Spaniards and Portuguese, the North Germans and South Germans, the English and Scotch”—were often the ones who fought most bitterly.

The explanation for this, to him, was "the narcissism of the small difference.” In other words: "It is precisely the minor differences in people who are otherwise alike that form the basis of feelings of hostility between them." This might be because we tend to remember and value the differences between ourselves and others more than we do the similarities. To this day, Freud’s theory is used to explain the factors behind certain civil wars.

It also applies to families: Let’s say you and your mom look and act alike, so much so that people sometimes mistake you for sisters. But she voted for Romney, and you’re always attending minimum-wage rallies, so no one inflames your righteous indignation like she can. You might like all the same rom-coms, but whenever she starts up about welfare queens, she might as well be a 90s-era Serb, and you, a Croat.

Chris Logan, a senior lecturer in psychology at Dallas’ Southern Methodist University, explains that if we and our family members have, “a lot of overlap in characteristics and a high desire for uniqueness, we will focus on those points that make us different. When we are all sitting around the same table, eating the same food, celebrating the same event, wearing the same terrible sweater, trying to justify our life choices to our parents, we might naturally focus our attention on those things that differentiate us from the others.”

Felder has written that when our relatives are different in a bad way, we might even see it as a reflection on ourselves. And the fact that you’re blood related to an incorrigible homophobe might be too much to bear.

Social Allergens

Then again, it might not be a relative’s worldview that’s so bothersome, but a particular habit—one that’s innocuous at first but becomes grating long before dessert is served. For instance, why does Grandpa Fred always have to tell the same Reader’s Digest joke about the hollandaise sauce?

In his book Annoying: the Science of What Bugs Us, Joe Palca describes these tendencies as “social allergens": “Small things that don't elicit much of a reaction at first but can lead to emotional explosions with repeated exposure.”

“Cumulative annoyances are one of the major triggers of relationships conflicts,” Logan said. “Conflicts are often triggered by repetition of certain small behaviors.”

As University of Louisville psychologist Michael Cunningham told Palca, these can range from uncouth habits, such as knuckle cracking, to inconsiderate acts, like checking your phone mid-conversation. The allergens that seem likeliest to surface during the holidays, though, are “intrusive behaviors,” like when Aunt Edna reminds you repeatedly that she knows multiple single Jewish doctors.