Vigilance is key to the war on terrorism
We in Northern Ireland know from long and bitter experience that the advantage always lies with the terrorists. They can plot and pick their target, choose a time to attack and then melt back into the general population to make their escape.
As the IRA infamously said after the attack on Mrs Thatcher and her Cabinet in Brighton in 1984, the terrorists only have to be lucky once, their would-be targets have to be lucky all the time.
It is the same with international terrorism. The new year had scarcely begun when an Islamic State gunman murdered 39 people and wounded many more in a Turkish nightclub.
This particular band of fanatics - who are all the more dangerous because they do not fear dying themselves - have spread their terror tactics throughout the Middle East and in parts of Europe, especially France, Germany and Turkey.
Not only do the targets vary, but so do the tactics - murder by gun or suicide bomb or by simply driving a lorry into a crowded area, as in Berlin or Nice.
The template for mass murder was set by the Middle Eastern terrorists who flew planes into New York's Twin Towers on September 11, 2001, killing almost 3,000 people.
Can anything be done to halt the terrorists? The intelligence war against terrorists of whatever hue is the most vital weapon in the armoury of democratic countries.
While the West may be engaged in bombing Islamic State strongholds in Iraq and Syria, such is the fanaticism of IS members that they almost welcome the blood sacrifice that entails. It confirms their belief that they are a just cause under attack from infidels.
There is no doubt that concerted military action against IS can weaken it, but it cannot halt attacks such as that carried out in Turkey.
The best defence against the terrorists is continued vigilance by the intelligence services and security forces, and the passing on of information by members of the public. We don't know how many acts of terrorism are disrupted by the security forces across Europe. Sadly we usually only learn of those that succeed.
But just as we did during the Troubles, people must refuse to be cowed by the terrorists. Certainly, they must be attuned to possible dangers, but if they allow life to be disrupted unduly then the terrorists have won. Terrorists, by definition, depend on spreading fear.