(Berkeley, CA) Yesterday, I heard two different American colleagues quote a story by the same Egyptian democracy activist. First, he said, there was lots of online activism against the Egyptian regime: people commenting, posting links, and “liking” each others’ comments. Then, when the Mubarak government blocked the Internet, the online advocates went onto the streets. And it was their street protests (combined with the nonviolent reaction of the army) that toppled the regime. Bottom line: “The best thing Mubarak did was shut down the Internet.”

I suspect the first phase of Internet activism was essential, for a particular purpose. It let everyone know that there was a potential mass movement. The inability to tell whether other people are at the point of acting is often a barrier to popular action. Still, even if you know that other people are angry, you can’t tell from their Tweeting and Facebook-posting whether they would actually put their lives on the line. Not knowing, you may fear to act.

That impasse had to be broken by a decisive signal that it was time to revolt together. And Mubarak (ironically) gave the signal by shutting down the Internet. It was a particularly powerful signal because all the energy that people had been expending online had nowhere to go–unless they went into the streets.

The lesson for dictators: don’t suddenly shut down the Internet. (Although the situation in Egypt may never be replicated exactly.) The lesson for activists of all stripes: you need a powerful signal and incentive to move people offline, once you have critical mass of supporters. If there is no dictator to provide the signal for you, you’ll have to find a way to do it yourself.