ANALYSIS: With each attack come millions of words. Politicians, journalists and witnesses express their shock and their determination to hold tight to the values of openness, tolerance and democracy.
But soon after these initial reactions, bewilderment sets in. What do the jihadists want? Why are they so brutal, as they were in Paris? How can they be stopped? How long can they endure?
More on the Paris attacks
The West's dilemmas are acute. But the jihadists also have things to worry about.
The mass movement of Syrian refugees tells its own story. While a few thousand alienated young men and women have headed east to Syria, hundreds of thousands of Syrians have headed west to Europe.
In the months that followed the fall of Mosul, there were signs the so-called Islamic State (IS) had learnt an important lesson about how to govern.
It knew the Taliban administrations in Afghanistan and small pockets of Pakistan had failed to sustain popular support.
In both countries, people had hoped the Taliban could offer an alternative to the existing, corrupt political order.
But when they gained power, the Taliban's brutality alienated its support base.
Take the issue of administering justice. Exasperated by the dysfunctional state judicial system, people wanted to believe in the Taliban's promises of speedy justice. But as often as not, the new religious courts consisted of ill-educated clerics handing down capricious verdicts.
There were signs when Islamic State started taking territory in Syria, it tried to avoid such mistakes. Local level administrators reassured traders they would be able to run their businesses in a safe and secure environment.
But, while first-hand accounts are few and far between, the evidence suggests IS has failed to follow through on such promises.
Furthermore, its leaders are so ill-educated, they will never be able to govern well enough to provide people with jobs.
When the Iraqi town of Sinjar was recently retaken by Western-backed Kurdish forces, there was no-one living there. Having killed or terrified Sinjar's residents, IS had ended up running a ghost town.
Flee or keep your head down
There are other reasons to believe IS will eventually fail.
Its central idea - those who do not agree with its religious ideas are worthy of death - is rejected by virtually everyone, including most Muslims.
For members of a minority seeing IS forces heading in their direction, it means the only option is to flee. For Sunni Muslims, it is a case of keeping your head down, attending prayers and obeying all the IS rules regarding dress, beards and other customs.
But right now, the victories just keep coming at an astonishing rate. Before 9/11, advocates of jihadist violence were little-known, irrelevant figures: misfits on the margin, rejected by their own societies and ignored by the West. How different it looks today.
The Americans have been humbled in Iraq and Afghanistan. The caliphate has been established. Al-Shabab in Somalia and Boko Haram in Nigeria have attracted tens of thousands of fighters. And all the while, the West looks on, transfixed, unsure what is coming next.
Of course, the jihadists have had setbacks. Osama Bin Laden was killed. Some drone strikes have found their mark. The West's proxy forces in Iraq and Syria have on a few occasions forced IS to relinquish territory.
But for the most part, the defeats have been Western ones. A single week can now bring hundreds of deaths.
'Us or them?'
To maintain the flow of recruits in the long term, the jihadists need to make Muslims feel more vulnerable and alienated in Western societies.
And in countries such as the UK, this objective is being achieved.
Largely unnoticed by the national media, inter-communal tensions are deepening at the local level. Where once the BNP stood alone, there are now a plethora of British - or more often English - nationalist groups resorting to street power.
Each protest makes it easier for the jihadist recruiters to press home the question: "Who are you with - us or them?"
The jihadists have another, more important, objective: to draw Western armies back to the Middle East.
Only then, will they be able to rally mainstream Arab support by portraying foreign troops as imperialists determined to occupy Muslim lands. Western governments will then be faced with the choice so concisely described by an al-Qaeda magazine headline in 2009: "Disastrous occupation or humiliating withdrawal?"
Each attack on a Western city increases the pressure to transform the air campaign against IS into a ground war. And everyone knows another major attack on US soil would almost guarantee the American military walking into IS's trap.
Regimes that terrify their subjects can persist for long periods of time. But history, all the way from the Soviet Union to Cambodia, suggests eventually they collapse.
The question for those now living in the caliphate - and for Westerners who want to go out for a drink on a Friday evening - is: "How long will it take? Years or decades?"
And in the meantime, the jihadists' strategists count their victories.