London - A strong relationship can deal with differences over religion, politics and even the in-laws.
But what can really spell disaster are disagreements with your other half over Five Roses or Glen Tea – or whether Omo is better than Ariel.
A study has found that couples who disagree over household brands could sour their relationship even more than those tackling different backgrounds, religions and personality traits.
And being forced to have your partner’s choice in muesli, yogurt or tomato ketchup can weaken a relationship in a manner compared to "death by a thousand cuts".
Researchers say that a disagreement about rival brands can lead couples to have a power struggle over whose favourite they will buy, with the partner who loses nursing a feeling of ‘low power’ that can last for years.
When a couple has a major difference between them, such as religion or politics, they know this from the start and can either work through it or split up, the researchers claim. But the partner who, for instance, prefers Coca-Cola but finds the fridge only ever has Pepsi feels that they have less power in the relationship, leading them to become progressively unhappier as the years go by, according to the study published in the Journal of Consumer Research.
US business academics from Duke University, in North Carolina, analysed the preferences of couples where one had a feeling of low power within the relationship.
And they found those who had this feeling were often stuck with their partner’s preferred brands when it came to soft drinks, beer, coffee, chocolate and even cars.
Marketing professor Gavan Fitzsimons said: "People think compatibility in relationships comes from having similar backgrounds, religion or education. But we find those things don’t explain how happy you are in life nearly as much as this notion of brand compatibility."
Couples with brand differences rarely seemed to split up as a direct result of this – but it had a drip-drip effect on the relationship over the course of many years, the researchers said.
Danielle Brick, a co-author of the study, said: "If you are lower in relationship power and have different brand preferences than your partner, you’re probably going to find yourself stuck with your partner’s favourite brands, over and over again.
"This could lead to a death-by-a-thousand-cuts feeling.
"Most couples won’t break up over brand incompatibility, but it leads to the low-power partner becoming less and less happy."
She added: "If you are a different religion than your romantic partner, you know that if this is an issue you can’t work through, then the relationship isn’t going to last. Conversely, if you like Coke and your partner likes Pepsi, you’re probably not going to break up over it – but 11 years into a relationship, when he or she keeps coming home with Pepsi, day in and day out, it might start to cause a little conflict.
"And if you’re the low-power person in the relationship, who continually loses out on brands and is stuck with your partner’s preferences, you are going to be less happy."