I was at Union Square Ventures last week talking to Fred Wilson and Brad Burnham about—what else?—friendship. They have an equity stake in Twitter, and have devoted plenty of thinking to what makes it so insanely popular. I came back to Midtown with a new appreciation for it.

One of Twitter’s charms is that it demands almost nothing of us. Say you get an email from a friend with a link. There’s a certain expectation for you to watch it and to say thanks. It’s a homework assignment. So before sending an email, you go through a cost-benefit analysis. Will this person appreciate it, or view it as meddlesome homework (or a waste of time)? E-mail is work and obligation.

On Twitter, each of us can recommend a link. If you have 500 followers, maybe 50 of them see it. Maybe five of them take a look. Let’s say two appreciate it. The other three may be less likely to open your links in the future. Maybe one will “unfollow” you. But that’s ok. Each of us finds our own audience. But the key is that there’s little guilt or obligation associated with Twitter. It’s a managed pool of serendipity.

My question: Is Facebook fundamentally different? (For some reason I feel less free about posting stuff there.)

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