A researcher who interviewed hundreds of married women found the happiest "never bought into" a "dangerous fantasy"

The most confusing piece of advice in "The Real Thing," Ellen McCarthy's 2015 book about love and relationships, is also the sagest.

Summarizing the findings of a researcher who interviewed hundreds of married women, McCarthy writes: "The collective wisdom seems to be: 'Sometimes you will be miserable. This is the reality of long-term intimacy. Carry on.'"

It's confusing because, well, sometimes you will be miserable? Like, how often? And how often is too often?! Kind of leaves us hanging.

But in reality, it's impossible to quantify the health of a romantic relationship. Ultimately, it's up to you to decide how much and what sort of misery is tolerable - and whether there's enough joy involved to balance it out.

McCarthy is a Washington Post feature writer who spent four years covering weddings, love, and relationships for The Post. "The Real Thing" is a collection of the lessons she learned on the love beat.

The researcher who interviewed hundreds of married women is Iris Krasnow, author of the 2011 book "The Secret Lives of Wives." She told McCarthy that the No. 1 thing women who were satisfied with their marriages had in common was that they "never bought into the dangerous fantasy - the myth - of Happily Ever After."

In other words, maybe the important thing is not knowing exactly how many moments of misery qualify you for a divorce, but accepting that total happiness is hard to come by.

McCarthy also interviewed Diane Sollee, a marriage educator who explained that too many people have delusional expectations for marriage. They buy into the myth "that if you find your soul mate, everything will be fine."

Yet even if you believe in soul mates and believe that you've found yours, that hardly ensures a blissful union. McCarthy writes:

"[Sollee] wants couples who are getting ready to walk down the aisle to know - really know - that it will be hard. That there will be times when one or both of them want out and can barely stand the sight of each other. That they'll be bored, then frustrated, angry, and perhaps resentful."

She adds: "Diane also wants them to know that all of these things are normal."

Bottom line: Uncomfortable emotions and experiences are an inevitable part of a romantic relationship (and of life in general). Don't expect perfection, and you'll free yourself up to find something close to it.