myth

Opposites attract. A couple, in their differences, complements each other.

reality

Great relationships require identical core values.

You'll actually hear two schools of thought on this. One maintains that shared interests and similarity of temperament comprise the recipe for lasting compatibility. After all, the reasoning goes, when the initial sexual thrill wears off, you'll be glad you have in common that passion for backgammon and Star Trek reruns. Conversely, if you're the pinstripe type, then your beloved's penchant for body piercing is going to seem a lot less cute once the honeymoon is over.

The other school of thought maintains that if you can get bored with sex, then you can certainly get bored with backgammon and Star Trek as well. A person who is just like you has nothing new to contribute to your life, whereas your opposite will continually challenge you and shake you out of your rut. No individual possesses the full inventory of desirable qualities in a human being, so the best plan is to marry the qualities you lack. The body-piercer saves the pinstriper from a life of dull conformity while the pinstriper saves the body-piercer from tetanus and People's Worst Dressed List.

The debate has raged for as long as anyone can remember. It is never resolved because examples of successful marriages can be cited in support of both hypotheses. We're here to settle it once and for all by asserting that both sides have it wrong. Tastes, interests, temperaments, and personality types are simply irrelevant to the success or failure of marriages. In those areas, you may choose your opposite, your clone, or anything in between. Suit yourself. It doesn't matter.

What does matter is that you and your partner share identical core values. That's right: We said identical. The more closely your values match your partner's, the better your chances are of building a lasting, happy marriage. Any difference in your values is going to become a source of destructive conflict. Count on it. Even if you never argue about the value itself, believing you've simply agreed to disagree, the difference will surface in every quarrel you will have for the rest of your lives.

Values are the principles that guide our conduct in relation to other people. They express how we think we ought to behave toward others and how we think others ought to behave toward us. When we act out a value, we are doing our bit to make the world what we believe it should be, not necessarily what we believe it is. For example, many people cheat on their partners and get away with it. But if in your vision of an ideal world, spouses are truthful with one another, then you do not deceive your partner. That's a value, a principle that guides your actions regardless of whether you are happy about the potential consequences. In a constantly changing world, values serve as an anchor, a touchstone that we can always turn to when in doubt about what to do. They create the only clarity available to us in an ambiguous universe.

Values are black and white, all or nothing, and situation-neutral. If you really value honesty, then you tell the truth in all situations, not just when it's convenient. You can't imagine any realistic scenario in which you'd feel good about lying. If truthfulness is a value for you, then any lie you tell will cost you. Your self-esteem will be diminished by it, and so will your clarity about who you are. Compromising your values leads to a loss of faith in yourself and in the world. It leads to cynicism, depression, and, even sometimes, illness.

This is why married couples must agree on their core values about relationships, even if they disagree about everything else. People who live together usually make some compromises for the sake of domestic harmony. But values are the one aspect of a person that cannot be compromised — even slightly — without grievous injury to the integrity of the self. Compromise your values for your partner, and you lose yourself. Ultimately you are likely to lose the marriage as well. Marriage partners must therefore agree on their fundamental values because they will never be able to resolve a values conflict by splitting the difference. It is a given that if both partners are true to themselves, then the conflict will persist for as long as they are married.

Since values express our ideal of how relationships should be, a couple who shares values likewise shares a vision. Ask them to describe an ideal marriage, and they will paint nearly identical pictures. When two people are looking at the same "big picture," joint decision-making becomes easier. They agree on what outcome they want and have only to debate which alternative is mostly likely to lead to it. Having the same ideal in mind, they are more likely to achieve it. Shared values lead to shared goals.

Goals are specific things that you want to do, such as buying a house, taking an extended vacation, or starting a family. Unlike values, goals shift over time. You can change your mind about them or adjust them to accommodate your partner. Values are the ideals that influence your choice of goals. When you drop or change a goal, you do not change the underlying value.

Sometimes couples mistake shared goals for shared values. For instance, a couple might agree on the goal of attaining a certain income level. One partner values the pursuit of excellence in a meaningful career. She would want to work hard regardless of financial need and sees the income target merely as a measure of achievement. For the other it is seen as a means to an end — an early, secure retirement from a job that he finds meaningless. Although the goal is identical, the underlying values about work are actually the opposite. The clash of values will become painfully evident once the goal is attained. It is also likely to be expressed in conflicts about how to attain the goal. The partner who is pursuing security may pressure the one who values achievement to remain in a dead-end but lucrative job, compromising the very value that led her to set the income goal in the first place.

Values are the most permanent aspect of our character. Our tastes, interests, appearances, and even certain aspects of our personality all change over time. Core values don't. This might not seem obvious at first because many people change their religion, their political party, or their opinions about various issues. But all of these changes are themselves motivated by core values that go deeper than our opinions or affiliations. If you ask yourself why you changed your mind about an issue or dropped out of an organization to which you'd once felt loyal, you will begin to identify the core values underlying these decisions.

At the age when most people marry, they are not yet able to articulate their core values. They confuse values with opinions and, most especially, with parental "shoulds" and "oughts" internalized during childhood. As we mature, we throw off many of these internal shibboleths as our true values emerge. Nevertheless, our core values have been present all along even if, when we are young, we can't say what they are. Because they are permanent, values form the most reliable basis for a lasting marriage. The interests that you think you share with your...