The protesters were as astonished as they were angry. Not long before, no one imagined the regime was vulnerable. Now the streets were filled with millions of people marching and shouting. The Shah must go! For those struggling to understand what's happening in Egypt, and what will happen, the Iranian revolution of 1978-'79 is an obvious reference point. It's also handy for lazy pundits. The Shah used violent repression? Then violent repression will fail in Egypt. The Iranian revolution ultimately produced an Islamist government? Then Egypt is going Islamist. Pick your parallel and place your bet. These facile equations are useless. Iran is not Egypt, the Shah is not Hosni Mubarak, and 1979 is not 2011. Every event is unique. History is not math. But there is another way in which the Iranian revolution brings events in Egypt into focus. Go back and look at the months and weeks before the revolution and it's evident that essentially no one saw it coming. Not the Shah and his officials. Not the opposition. It was "unthinkable," said Mehdi Bazargan, the future first prime minister of the revolutionary government. The Central Intelligence Agency was also caught by surprise, despite the close watch it kept on a key American ally: A mere five months before the Shah was forced to flee, with protests growing steadily, the CIA reported Iran "was not in a revolutionary or even a 'pre-revolutionary' situation." For ordinary people -- the people whose presence on the streets would ultimately decide the fate of Iran -- the moment of crisis was both thrilling and terrifying. "Being in a revolution is such a confusing time," says University of North Carolina sociologist Charles Kurzman. "It's a time when you don't know, literally, what tomorrow will bring. If you plan to go to a demonstration, you don't know if you're going to be the only one out there, or one in a sea of millions. Whether the police will shoot you, or join you in the streets protesting against the regime." For his 2004 book The Unthinkable Revolution, Kurzman consulted a wide array of sources to see just what Iranians were thinking in the fateful months and weeks before the toppling of the government. There was overwhelming uncertainty. Coping with it was a constant struggle. "In order to deal with this uncertainty, I found that people are obsessive about talking politics," says Kurzman. "They talk politics with everybody. With their butcher. With folks standing at the bus stop. People they never really talked to, ever." Protests are a game of numbers. If huge crowds turn out, there is relative safety and a greater chance of success. If not, those present are more likely to fail. And die. Predicting what other people will do "is a matter of life and death," says Kurzman. So people talk politics with strangers, constantly. "They're trying to sample outside their family and friend network to find out what everyone else is going to do," Kurzman says. Should I go to the protest? Should I join the strike? Millions of people asked these questions every day. Their decisions depended on what they thought everyone else would do. And they could change right up until the very moment of acting. In this tense atmosphere, rumours and emotions surged through the population like electric charges. Excitement could give way to terror in an instant. Despair to hope. And back again. "You can't read off people's attitudes from a year before, a month before, even a day before, and predict what they are going to do on any given day under these circumstances," Kurzman says. Even what people wanted was liable to sudden, startling change. "What your end goal is depends on what you think is possible," Kurzman notes. "If the fall of a dictatorial government suddenly seems achievable, then that may be the most important thing in your life today. Whereas yesterday, it may have seemed pie-in-the-sky and you would go about your business and not even form an opinion about the topic because it seems so unviable." This is precisely what's happening in Egypt now. There are many possible outcomes. And no way of predicting which will actually happen. To everyone but cocky pundits and those who think like them, that may seem obvious. Even trite. But it's not. It's an essential insight. And it's likely to be forgotten. Because the drama will end, and when it does, the outcome, whatever it is, will feel far more likely than it does now. Psychologists call this phenomenon "hindsight bias." It's a big reason why people think the future is more predictable than it is. On top of this, experts will develop elaborate stories that claim to explain why what happened had to happen (Kurzman picks apart several such stories about the Iranian revolution). This, too, encourages us to think the future is more predictable than it is: If we can connect the dots after the fact, we should be able to do the same in advance. And if the outcome in Egypt could have been predicted but wasn't, it follows that someone blew it. The blame game will begin. Intelligence agencies, in particular, will be attacked for failing to forecast the storm, as the CIA was after the Iranian revolution. In fact, this has already begun. Israel's intelligence chief is now in hot water because, on the day the unrest in Egypt started, he told a Knesset committee that Mubarak's government was in no danger. "Remember this moment of uncertainty," Kurzman advises. It is a much clearer glimpse of the truth than what we will hear after the fact.