This is Hidden Brain. I'm Shankar Vedantam. When Harry Reeves was in middle school,

he cared what his classmates thought of him. Now all middle schoolers want to fit in with their peers.

But Harry, he was next level.

I was somewhat insecure as an adolescent, very unsure of my standing within the social group that I lived in.

And I would keep daily charts of how I was doing and who I connected with and who I did not connect with.

Harry's charts did more than track who sat next to him at lunch or who joked around with him in the hallway.

No, this is actually more embarrassing than that. These were actually graphs where I would rate on a ten point scale

how I had done with various people on that day. So if I thought that a certain person had really liked me on that day,

you know they would get a nine. And if I thought I'd really come across as an idiot with another person that might be a two or three.

And I would have these charts over time where the lines would go up and down.

It was a painful way to go through middle school. But it did come with an upside.

Years later, Harry learned there were people who kept such charts professionally.

I discovered, oh my god, there are people who actually make a life of studying this stuff.

And it just instantly grabbed me because it was something that I had always been doing.

Harry went on to become a social psychologist. And he discovered that if you keep meticulous charts,

if you track the ups and downs of relationships like an insecure middle schooler,

you can actually discover really interesting things about the air-bent flow of human relationships.

This week on Hidden Brain, the secret ingredient that makes some relationships thrive and others falter.

Many of us know what it's like to meet a soulmate or kindred spirit at work.

We know what it feels like to be inspired by a politician or a business leader.

But what exactly prompts us to feel this deep connection with some people, but not with others?

Is it having a shared goal, the intangibles of chemistry?

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