You’ve heard the expression, “opposites attract.” You’ve also heard that “birds of a feather flock together.” Two expressions of folk wisdom that are opposite and, yet, seem to be true. Yes, they both are true, at least somewhat. Opposites do attract -- but in spite of Hollywood movies in which two completely different characters live happily ever after -- opposites don’t tend to last.

Similar vs. Complementary Relationships

There are two types of relationships, writes Elizabeth Svoboda in her Psychology Today article, “Lessons for Living.” Homogamous relationships are those in which two people are similar. They have similar upbringings, similar religious beliefs, similar educational backgrounds, as well as similar political beliefs, attitudes and values. Complementary relationships are those in which the characteristics of one person complement the characteristics of the other -- you may be shy, whereas she is outgoing; you may be organized, whereas she is unstructured. Research shows that homogamous relationships tend to be more long-lasting and complementary relationships have more conflict.

A Similar Personality Is Key

There's a difference between having similar attitudes and beliefs and having similar personality characteristics. Attitudes are what beginning relationships are based on because they are fairly easy to determine, according to psychologists Shanhong Luo and Eva C. Klohnen, in their article, “Assortative Mating and Marital Quality in Newlyweds: A Couple-Centered Approach." Couples quickly discuss their views on important topics but long-term relationship satisfaction relies on similar personality characteristics such as intelligence, extraversion, curiosity and sense of humor. Personality characteristics are more difficult to determine and generally aren’t known until much farther into the relationship.

Someone Similar to You

Research shows that you tend to like the person who is most similar to you. Psychotherapist and professor Kristine Keller discusses the “balance theory” in her article, “Oil and Vinegar: Why Opposites Don’t Attract” as the reason for this. The balance theory states that you prefer people who share your thoughts, desires, and attitudes because it reassures you that your characteristics are normal and desirable. Research has shown that this is cross-cultural – not only is this true in the U.S., but also in the Middle East, South America, South Asia and East Asia.

Opposites Might Be Too Different

If relationships between opposites generally don’t last, why is this expression so often used? A couple of reasons exist as to why this folk wisdom has lasted so long, according to Scott O. Lilienfeld and Steven Jay Lynn et al, authors of “50 Great Myths of Popular Psychology: Shattering Widespread Misconceptions about Human Behavior." You’ve probably heard that your goal is to find someone who completes you and the only way to do that is to find someone who has something that you don’t -- such as opposite characteristics. Some opposite characteristics, such as if one person is more easy-going or more detail-oriented, can be a good balance in a relationship, writes Jean Lawrence in her WebMD article, "Do Opposites Attract?" However, if two people's values are different or they prefer to spend their time in different activities, that can cause problems long-term.