Developed countries must balance the certainty of safety with the practicalities of daily life.
Boston bombs show absolute security is myth
With one of the suspected Boston bombers dead and one in custody, the attention of officials, the public and the media now turns from the manhunt to the motive for this strange crime, from "who" and "how" to "why".
Both Dzhokhar and Tamerlan Tsarnaev spent their formative years in the US, and both were naturalised citizens. This has already sparked much soul-searching about what can be done to prevent such home-grown amateur terrorism in the future.
The answer is difficult to stomach: surprisingly little. The Arab world has spent decades attempting to stop attacks from both groups within their countries and actors from elsewhere. Even the most developed countries in the Middle East are at risk.
The truth of the modern world is that there is no escaping some level of risk of political violence or, as in this case, of what appears to be quasi-political violence for purposes that can at best be called confused. There are always elements, within and without, sane or not, that wish to inflict harm, and they can use the openness of our societies against us.
The idea of absolute security, for which many in the US seemed to yearn after the attacks of September 11, 2001, is one that developed countries will have to admit is practically impossible. Law enforcement agencies seem to have a good, if not perfect, record against major plots, but in the age of lone-wolf terrorism, there is always the possibility that one attacker, or two young brothers, will get through. The odds are asymmetric. Police and intelligence agencies have to be successful all the time, while attackers need to get through only once.
Indeed, although the Boston attack was the first deadly act of terrorism on US soil since 2001 (the shockingly regular gun massacres are not political), others have come close. Both "shoe bomber" Richard Reid in 2001 and "underwear bomber" Umar Farouk Abdulmuttalab in 2009 had in effect broken through all the security cordons America could erect. It was only by chance that they failed.
That does not mean security measures are useless - one of the reasons that terrorists go for soft targets like the Boston Marathon is the difficulty in reaching heavily guarded "high value" buildings and planes.
But it does mean that modern states must balance the certainty of safety with the practicalities of daily life in a free country. In the US and elsewhere in the West, security agencies have become increasingly controlling and invasive, all in the name of defending "freedom". Indeed there is the danger of an initial overreaction to last week's trauma.
The question for all of us is not how to live in absolute safety but how to get as close to that as possible without changing our way of life.