Why ‘Birds of a Feather’ Is Terrible Advice: New Research on Friendship

Why ‘Birds of a Feather’ Is Terrible Advice: New Research on Friendship

The old saying “birds of a feather flock together” suggests that the best friendships are built on similarity. But new research from Michigan State University shows this advice is mostly wrong. What actually makes a friendship satisfying has little to do with how much you have in common. Instead, the key lies in emotional intelligence and three simple traits: agreeableness, conscientiousness, and emotional stability.

What the Research Found

Hyewon Yang, PhD, and her team studied 371 friend groups of exactly four people (1,484 participants total). They used a “round-robin” design where each person rated their own personality traits, then rated their three friends, and finally rated how happy they were with each friendship. The results were published in Social Psychological and Personality Science.

Similarity Is Weak

Actual similarity between friends was surprisingly low. For four out of five personality traits, the correlation was only 0.05 to 0.10—a very small connection. There was no measurable similarity at all in extraversion. The one exception was openness, where friends did overlap more. But even then, people consistently overestimated how similar their friends were to them, projecting their own traits onto others who often didn’t share them.

What Really Predicts Friendship Satisfaction

Neither actual nor perceived similarity predicted how happy people were with a friendship. Instead, three traits stood out:

• Agreeableness – How easy and kind someone is to be around.
• Conscientiousness – How reliable and responsible they are.
• Emotional stability – How calm and steady they stay under stress.

In short, likability is more about emotional intelligence (EI) than about being alike.

How Emotional Intelligence Helps You Build Better Friendships

Emotional intelligence is your ability to recognize, understand, and manage your own emotions, as well as recognize and influence the emotions of others. It includes four key skills: self-awareness, self-management, social awareness, and relationship management. To improve your EI, experts recommend taking a psychologically validated assessment.

The ACE Filter: A Simple Strategy

When meeting new people, use the ACE filter. ACE stands for:

• Agreeableness
• Conscientiousness
• Emotional stability

Most of us naturally use a “similarity shortcut”—we feel comfortable with people who share our background, music taste, or politics. But this shortcut is a poor predictor of long-term friendship happiness. ACE traits give you much better information, and none of them require the other person to be anything like you.

A Practical Example of ACE in Action

Imagine you’re new to a city and meeting people through a rec league, book club, or neighbor’s barbecue. Your instinct might be to gravitate toward whoever laughs at your jokes or shares your hobbies. Instead, ask yourself these questions:

• Emotional stability: When this person is stressed, do they stay calm or get overwhelmed?
• Agreeableness: When plans change, are they easygoing or difficult to deal with?
• Conscientiousness: Do they follow through on small promises?

You don’t need to ask these questions directly. Just keep them in mind as you get to know someone. And to improve your own likability, flip the questions: Are you calm under stress? Are you flexible when plans change? Do you keep your word?

Putting This Research Into Action

Friendship satisfaction isn’t about finding your mirror image. It’s about finding people you can truly rely on. Next time you’re deciding who to spend time with, skip the similarity test and use the ACE filter instead. Look for agreeableness, conscientiousness, and emotional stability. These are the traits that make a friendship feel good and add real value to your life.