Consider the case of Maureen Evans. A grad student and poet, Evans got into Twitter at the very beginning — back in 2006 — and soon built up almost 100 followers. Like many users, she enjoyed the conversational nature of the medium. A follower would respond to one of her posts, other followers would chime in, and she’d respond back.

Then, in 2007, she began a nifty project: tweeting recipes, each condensed to 140 characters. She soon amassed 3,000 followers, but her online life still felt like a small town: Among the regulars, people knew each other and enjoyed conversing. But as her audience grew and grew, eventually cracking 13,000, the sense of community evaporated. People stopped talking to one another, or even talking to her. “It became dead silence,” she marvels.

Why? Because socializing doesn’t scale. Once a group reaches a certain size, each participant starts to feel anonymous again, and the person they’re following — who once seemed proximal, like a friend — now seems larger than life and remote. “They feel they can’t possibly be the person who’s going to make the useful contribution,” Evans says. So the conversation stops.

Evans isn’t alone. I’ve heard this story again and again from those who’ve risen into the lower ranks of microfame. At a few hundred or a few thousand followers, they’re having fun — but any bigger and it falls apart. Social media stops being social. It’s no longer a bantering process of thinking and living out loud. It becomes old-fashioned broadcasting.

The lesson? There’s value in obscurity.

After all, the world’s bravest and most important ideas are often forged away from the spotlight — in small, obscure groups of people who are passionately interested in a subject and like arguing about it. They’re willing to experiment with risky or dumb concepts because they’re among intimates. (It was, after all, small groups of marginal weirdos that brought us the computer, democracy, and the novel.)

Technically speaking, online social-networking tools ought to be great at fostering these sorts of clusters. Blogs and Twitter and Facebook are, as Internet guru John Battelle puts it, “conversational media.” But when the conversation gets big enough, it shuts down. Not only do audiences feel estranged, the participants also start self-censoring. People who suddenly find themselves with really huge audiences often start writing more cautiously, like politicians.

When it comes to microfame, the worst place to be is in the middle of the pack. If someone’s got 1.5 million followers on Twitter, they’re one of the rare and straightforwardly famous folks online. Like a digital Oprah, they enjoy a massive audience that might even generate revenue. There’s no pretense of intimacy with their audience, so there’s no conversation to spoil. Meanwhile, if you have a hundred followers, you’re clearly just chatting with pals. It’s the middle ground — when someone amasses, say, tens of thousands of followers — where the social contract of social media becomes murky.

Maybe we should be designing tools that reward obscurity — that encourage us to remain in the shadows. Or what if they warned us when our social circles became unsustainably large? Sure, we’d be connected with fewer people, but we’d be communicating with them, and not just talking at them.