Editor’s Note: Juliette Kayyem, a CNN national security analyst, is a professor at Harvard’s Kennedy School of Government, a former assistant secretary in the U.S. Department of Homeland Security and founder of Kayyem Solutions, a security consulting firm. She is also the host of the Security Mom podcast. The opinions expressed in this commentary are hers.

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Juliette Kayyem: Let's praise the train heroes for their courage in this particular situation

Still, she says, we should realize that sometimes the right thing to do isn't to engage but to flee

CNN  — 

Spencer Stone. Alek Skarlatos. Anthony Sadler. If I ever find myself in trouble, I hope the three of you are close by.

These Americans, whose seemingly inconsequential vacation to Europe became the stuff of hero-making, bravely tackled an armed terrorist on a Friday train heading to Paris. The terrorist, identified as Ayoub El Khazzani, of Moroccan origin, was carrying an assault rifle, a pistol and a box cutter and apparently had every intention of causing major fatalities on the train filled with business and summer travelers.

Juliette Kayyem

Stone, Skarlatos and Sadler – the first two have military training – heard the early commotion on the train and seemed to know exactly what to do. Skarlatos, just returning from Afghanistan, is said to have turned to Stone and said, “Let’s go, go!” They, with the aid of French and British passengers, took El Khazzani down, suffering injuries in the process.

A very serious scuffle ensued, as the terrorist seemed determined to stage a rampage. Eventually, he was isolated, the train stopped and the three men – after tending to other injured – emerged as the only people between life and another terrorist atrocity in France.

This is not what Sadler imagined when he wrote in a May Twitter post, “I’m going to Europe!!!! Like wow.” The epic story gets even more dramatic, as French actor Jean-Hugues Anglade cut himself while he broke the glass to initiate the train’s alarm system. Like wow.

Heroes are never born, they are made and the three young men deserve every accolade they are now getting. But while we might all want them as traveling companions, that’s a rather unrealistic solution for the risks we face. So from their story emerges a series of lessons, some even controversial, to learn and adapt.

As this case shows, in some circumstances, engaging the enemy is not a matter of choice: on an airplane or a train where mobility is confined, it may be the right move. But it is wrong to think that is the only wise move in most terror situations.

Sometimes, it is smart to run. Each case is so different. The 2009 Christmas attack on an airline landing in Detroit was stopped by a fellow traveler. The 2010 Times Square bombing was foiled when a street vendor noticed smoke in a car and alerted police. But, as we all remember, even heroes can fail despite the noblest of efforts, such as those on Flight 93 on 9/11.

This is simply to say that what happened on that train, in a confined and moving space, is not applicable in all circumstances. For example in almost every training session for active shooter cases – especially at colleges and universities that have seen their fair share of them – the general rule is to run. Don’t hide; don’t engage; don’t stay put. Exit as fast as you can.

Each incident is so fact-dependent that to extrapolate this case – where it appears one of the guns jammed and the other wasn’t properly assembled – to a single lesson learned gives too little consideration to the unique circumstances each case entails.

Second, training of transportation workers is no joke but is too often treated as such. From accounts so far, the train personnel were slow to respond and slow to communicate the harm. In a time when there is little stability, and solo actors can emerge as mass killers just by purchasing a train ticket, transportation workers are front line responders. The United States has done much to focus on mass transportation security – port, train and of course air travel – for obvious reasons, but a police presence is never going to be able to replace engaged and trained employees.

Finally, while there is no question that greater security is needed for urban train travel, most modes of transportation are going to be inherently vulnerable. This is not to forgive the shocking realization that a heavily armed man got onto a major train line completely undetected. But as we build stronger transportation defenses, it is unlikely a single solution will emerge. There will have to be layered security in the hopes that, together, the risk can be minimized.

The reason why: It is clear that the market talks, and since 9/11 as security has increased for airline travel, more and more customers are using our rails for shorter distances because of the convenience. There is no major metropolitan train or commuter system that could sustain the kind of security we have come to expect for air travel; the system would just shut down, impacting commerce and our global economy. And even if we were to make train travel less of a soft target, those searching to do harm would just move to other modes of transportation, such as buses. Indeed, in London’s subway terror attacks, one of the terrorists quickly moved to detonate his bomb on a bus when the London Underground was shut down after the first bombs went off.

It is likely that in the days to come there will be no shortage of those seeking seemingly obvious solutions to a problem that does not have a single fix. As an interconnected global economy, we will always be in movement, balancing risk and reward. We will always be vulnerable. Unless, of course, Stone, Skarlatos and Sadler are traveling nearby.

The images flooding in of Thursday morning’s stampede in Saudi Arabia tell a horrifying tale. Hundreds of people have suffered a gruesome death as they were crushed or trampled during a stampede that occurred at the annual pilgrimage of devout Muslims to their holy city of Mecca.

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