Friends show only weak personality similarity, and none in extraversion.

People consistently overestimate how similar their friends really are.

Matching personalities didn’t predict how happy people are as friends.

What matters instead: agreeableness, stability, and how you see them.

"Birds of a feather flock together" is one of those sayings repeated so often that we stop questioning it. We assume it, we build friendships expecting it, and we rarely ask whether it's really true, or whether it's the reason those friendships work in the first place.

A study published this month decided to check (Yang et al., 2026). Researchers recruited 371 real friend groups of exactly four people each, verified over video call, and had every participant rate their own personality and each friend's personality across the Big Five traits: openness, conscientiousness, extraversion, agreeableness, and emotional stability.

The overlap was........

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