Last week I was invited to a wedding shower where the guests were asked to bring a note card with one piece of advice for the new couple.

Most of the cards had typical comments like "Always compromise," "Be honest and truthful," or "Never go to bed mad." As a relationship expert, I knew that the majority of the advice was not supported by scientific findings. So I began to wonder: how much of what people know about relationships is repeated as fact but is more like fiction?

We have learned about relationships from movies, TV and magazines, family and friends. And, of course, we've learned a thing or two about love firsthand. But without realizing it, we tend to cling to strong opinions about love and marriage based on misconceptions and myths. These misconceptions and myths can sabotage our relationships by creating unrealistic expectations that are bound to lead to frustration, anger, and sadness.

In my book, "5 Simple Steps to Take Your Marriage from Good to Great" (Random House, 2009), I discuss one important trait that happy couples in my long-term study share: they have learned how to have realistic expectations of their relationships and partner. To take your relationship from good to great, it's essential to transform unrealistic expectations -- the ones that rarely get met and then cause you frustration, anger, sadness, hurt, and other negative emotions -- into more realistic versions that will be met. One of the best ways to do that is to stop relying on myths and look at facts instead.

Let's look at some common relationship myths that might be contributing to unrealistic expectations. By learning the facts about how men and women relate, behave, and think, you can approach your relationship with fresh, unbiased knowledge. And, next time you're invited to a friend's shower or asked to help a friend or family member, your advice will be based on fact rather than fiction!

1) Myth: Opposites attract and are more likely to stay interesting to one another over the long haul.

Fact: My research and that of others show that similarities are what actually keep people together for the long term and lead to the most successful, happy relationships. In my study, happy couples might have very different tastes in music, different social backgrounds, or even different religious, but the key aspect they shared was similar basic life values. This is the similarity that counts.

The take-away: If you want to find someone to grow old with, look for someone who has values that are compatible with yours.

2) Myth: A perfect relationship means no conflict.

Fact: A lack of conflict in a relationship signals that you may not be dealing with issues that really matter. In a surprising finding from my long-term study of marriage, the couples who reported no tensions or differences about money, family, spouse's family, leisure time, religious beliefs, or children were not very happy over time.

The take away: Don't shy away from difficult conversations. Learning how to disagree in a healthy, productive manner is a key component of happy relationships.

3) Myth: Having separate lives keeps couples together long term.

Fact: Interdependence -- social, emotional, and financial -- is what creates the incentive for couples to stay together. It's also important to be independent, to have your own interests, activities, and friends. This adds excitement and freshness to relationships. But couples who live parallel lives and don't invite their spouse into their world on a regular basis tend to grow apart and be unhappy over the long term.

The take-away: Couples who work on acquiring common interests as the years go by are much happier than those in which each partner gets increasingly involved in a separate set of activities.

4) Myth: To be happy, you need to talk about relationship challenges and problems often.

Fact: In order for intimacy to occur in a relationship, both partners need to share and disclose concerns from time to time. But be careful about how much time you spend on conscious relationship maintenance, because men and women have very different tolerances for "relationship talk." Women, as a rule, have a positive association with relationship talk; it makes them feel connected and happy. Men, on the other hand, do not enjoy relationship talk; it makes them feel blamed, worried, and distressed.