Why now? Why have hundreds of thousands of Serbs gone out on the streets in recent weeks? There is a chemistry at work, but it is a mysterious chemistry. Many elements - poverty, fear, resentment, hopelessness - are combined.
Just below the hotel room where I am now sitting, I have in past years stood amid demonstrators in Belgrade, and asked myself and others whether, this time, the protests will gain unstoppable momentum. Each time, we shrugged and admitted ignorance. It seemed unlikely, given the apathy around us.
Slobodan Milosevic, the Serbian president, has always been a master of tactics. Now, at last, he may have over-reached himself. Throughout the years of the Yugoslav wars, the protests in Belgrade remained relatively small. Serbs, who in the Second World War had shown enormous bravery in the struggle against the Nazis, seemed passive in the face of a demagogic leader of their own.
The pattern of events in other countries has shown, however, that even the most ap- parently compliant population can finally be goaded into pro-test, when the time is right. In Czechoslovakia, people sat almost quiet for 20 years after the Soviet invasion of 1968, licking their wounds and adjusting to the new realities. A few thousand demonstrated in August 1988. At the end of October 1989, a crucial demonstration in Prague was too small to get the ball rolling - through a mixture of apathy and fear.
But, less than three weeks later, another demonstration got thousands of students out on the streets and ignited the spark. The turning point: police beat up demonstrators, and one man was thought to have been killed. At which point those Czechs who had been muttering words of loyalty one day were out on the streets the next.
The use of violence, intended to intimidate, had the opposite effect.
In East Germany, as in Serbia, a fake election result triggered the opposition demon- strations which eventually brought the regime down. The local elections in May 1989 were rigged even more shamelessly than usual. The Leipzigers were ready to do something about it. Through the summer and autumn, numbers attending Monday demonstrations kept increasing. When the regime began to panic, it decided to use the Tiananmen Square option, which it believed that Peking had so successfully used in June. Un- fortunately, this was the crunch: when people realised that the authorities were ready to shoot, more, not less, of them decided to risk their lives. The regime's thuggishness persuaded many to show bravery on that 9 October in Leipzig.
In Latvia, one night before an expected assault by Russian troops in February 1991, I met an elderly couple dancing in the packed city streets: they partied their way through the night, so that their presence, and that of thousands of others, might make the political cost of a military assault unacceptably high.
They were infectiously happy, although I am sure they did not consider themselves brave. The Soviet troops had killed before (in Lithuania), and were about to kill again (in Latvia).
In democracies, we find it difficult to imagine risking our lives for our beliefs. Going on a de-monstration is a luxury or a dull duty, not a necessity. If demonstrators in London or Manchester thought they might be killed, going out on the streets would seem as foolish as chasing a lost dog over thin ice.
When the going gets tougher, the decisions, in some respects, get easier. In Stalinist times, it was literally suicidal to defy the authorities. But in less obviously murderous regimes, the risks are worth weighing up. Indeed, it sometimes seems that there are no real choices. As the old saying put it: if not now, when?
In Serbia today, the balance seems to have been tipped. Slobodan Milosevic is not finished. But he is living on borrowed time - partly because of those who have been ready to risk the potential violence. There must now be room for hope that a true history of Serbia, and of its ignominious leader, will one day be written for the next generation of young Serbs.