IN the hours after the terrorist attack on Parliament, a four-word phrase began trending on social media that was all the more eloquent for its simplicity.
We Are Not Afraid. The term spread at lighting speed, across London, then Britain, then Europe, America and to every corner of the world that has been blighted by terrorism.
So very few words, but how loudly and eloquently they proclaim a spirit of defiance and stoicism that no atrocity, however horrific, can ever snuff out.
Those words were repeated in the House of Commons by the Prime Minister, and as she spoke them, the people of London were living them.
They left their homes as usual, caught the Tube or the bus and went to work, carrying on as normal, just as they did 12 years ago after the July 2005 bombings.
Not cowed by fear, not glancing apprehensively over their shoulders, not worrying that a car was going to be deliberately driven at them, but simply getting on with their day.
And in doing so, millions quietly – and without fuss – demonstrated why the terrorists can never achieve their aims, however barbaric the methods they employ.
In 2005, a group of worthless maniacs – three of them from Yorkshire and with nothing to offer except futile nihilism – attempted to change the way Britain lives, and failed.
Self-indulgent videos left behind with messages intended to justify their actions exposed the terrorists for what they were – dim-witted inadequates deserving of nothing except derision.
Another contemptible inadequate tried and failed on Wednesday. How spectacularly he failed was apparent in the throngs of people determined not to be intimidated, getting on with their lives and jobs, even as their hearts went out to the victims.
Somewhere in the twisted psyche of Khalid Masood, who drove at pedestrians and then murdered PC Keith Palmer, was probably the notion that he was striking at the heart of democracy and freedom.
The beating of that heart did not falter for even a millisecond, and never will in the face of terrorism.
Britain’s refusal to walk in fear bore witness to that, as did the words of MPs from all sides as Parliament got on with its business and rightly refused to rush into decisions about how its security will be increased.
Security will have to be tightened for all of us, whether we live in Yorkshire or the capital.
But it won’t change us. It won’t fundamentally change how we live, or go about our daily business, any more than the IRA terrorism of the 1970s and 80s did, or the 2005 bombings.
Nor will it change the openness and freedom of our society, which is one of the privileges of living in Britain too often taken for granted.
We may have to get used to seeing more armed police on our streets. So be it. They will come to be seen not as totems of the threat from extremists, but a presence as reassuring as the old-fashioned bobby on the beat who greets passers-by.
There may have to be tighter control of who can get into the grounds of the Palace of Westminster. Sensible enough. But it won’t stop parties of schoolchildren being taken there, nor distance MPs from their constituents.
Britain will adapt, but not change. We’ve all adapted to the stringent security checks at airports introduced after the September 11 2001 attacks on America, but it hasn’t put us off flying.
That instinctive refusal to change means the terrorists will always fail in their aim to make us live in fear.
We mourn their victims, mark anniversaries with respect, but we honour their memories on a daily basis by carrying on with life as they would have done.
Shocking though the attack was, in a sense it came as no surprise. There was a certain inevitability that London would be targeted again by the current wave of Islamist terrorists, a question of when rather than if.
The threat level has long been rated as severe, and it is likely to remain so for the foreseeable future.
When police completely unravel the thread of perverted ideology and hatred that led to Westminster Bridge and the threshold of Parliament, the chances are it will be a familiar story.
The toxic mix of adulation for the bloodthirsty savages of Iraq and Syria with their propensity for medieval violence, lunatic propaganda on the internet and an irrational hatred of the liberal societies of the West will, as likely as not, be a feature.
The police and security services deserve our thanks for all they do in foiling plots. Theirs is a never-ending struggle, waged in the shadows, and rooting out those who show few outward signs of developing into terrorists is fiendishly difficult.
Their task is made all the harder if we are now seeing a move towards low-tech terrorism by so-called lone wolves, when vehicles are used as weapons, as they were in Nice and Berlin, as well as London. Such terrorists are more difficult to track than groups involved in complicated plots.
That lurking threat, especially since the wave of attacks in France and Germany, means that Britain is psychologically prepared to cope with terrorism – and deal calmly with its aftermath.
There are those who would argue that Britain’s national spirit is not what it once was, that our increasingly diverse society lacks cohesiveness and a common sense of right and wrong. The response to what happened in Westminster puts the lie to that.
From the people who ran to help victims in the moments after the attack – with no thought for their own safety – to the calm and unruffled way that millions instinctively knew that the only possible response was to carry on as normal, this was Britain at its best.
Such a spirit is indomitable, and the best possible riposte to those who would kill and maim. We Are Not Afraid. As a national motto in the face of unpredictable threats, it could not be bettered.