Why do some marriages last a lifetime, while some end in divorce? For every pair of marriage lifers (think Paul Newman and Joanne Woodward), there's a couple like Kim Kardashian and Kris Humphries, barely making it through two months. Why, though? Are there some behaviors that are just universally destructive to a marriage?

On Wednesday, we asked our followers on Facebook and Twitter to share with us the reasons they think marriages end in divorce.

The responses ranged from a lack of sex, to a lack of positive interaction -- one reader even devised a formula: according to him, if there are less than five positive interactions for every one negative interaction, you're in trouble.

Click through the slideshow below to read the responses, then head to the comments to tell us why you think marriages end in divorce.

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