Sometimes I'll have a friendly interaction with somebody but then go away feeling a bit off or sad. It occurred to me that the feeling is the realization that the other person doesn't consider me a friend or perhaps doesn't care about me at all, despite the friendly interaction we just had.

There are cues to pick up on. There's either a mutual curiosity and concern, or not. When you part with the other person, you may arrange to meet in the future, or in some way continue the relationship. And it doesn't have to do with how long you've known a person – I've met people who were immediately interested and willing to connect. I've known people for years who never open to more than the occasional friendly interaction.

And lately I've been saddened to experience this coldness more often. Even among people I regularly interact with, there is this unspoken boundary. Maybe we play music together, but there's an understanding that we won't care about each other beyond that. Or we volunteer together and have cordial conversations, but shouldn't expect to be invited to somebody's house.

Come to think of it, I remember experiencing this in high school. I had friends – but not close friends. It was rare to be invited to someone's house. Sometimes when I was invited, we'd meet in a living room. I never saw my friend's bedroom, which I found odd. In elementary school, when friends visited each other, there wasn't any protectiveness or much privacy. Do kids develop their boundaries in high school, when the social risk of embarrassment feels much higher? Is that when we learn to keep most people at a safe distance?