Recently, the world woke up to yet another terrorist attack in Europe. A small group of men had killed several people and wounded many others. The victims were simply in the wrong place at the wrong time. They did nothing to deserve the attack, and had no warning. It could have been you or me, and that’s the point.

Terrorism acts are usually small in scope. The number of people killed or injured are fewer than those killed in traffic accidents on that particular day. The force of terrorism cannot defeat an army or take over a country. So, how does it work?

The most obvious impact of terrorism is psychological. Those survivors in the immediate vicinity of the attack will often experience Post-Traumatic Stress Disorder (PTSD), and family members of the deceased experience grief. More broadly, however, the terrorist attack impacts the psychological well-being of the entire society.

As humans, we maintain a constant background impression of our relative safety. We have a general sense of how safe we are in any particular situation. We tend to feel safer in our homes than we do in public places, safer in our hometown than when traveling, safer when surrounded by friends than when in the company of strangers, and so on. Of course, we feel safer in our daily routines than we would if we were soldiers fighting in a war zone.

Terrorism disrupts this impression of safety. Watching a terrorist attack, where people were killed or wounded while carrying on their daily routines, eliminates our assumption of safety. These victims weren’t fighting in a war. They weren’t doing some dangerous activity. They were doing what we all do. They were busy living their lives. If it can happen to them, it can happen to us.

Our estimation of the danger is exaggerated by our distorted perceptions of probability. When we see an event occur, we tend to overestimate the probably of it happening again. This can be illustrated in several ways. Watching news coverage of a plane crash creates the feeling that planes crash frequently. This feeling can occur, even when we remind ourselves that thousands of planes take off and land every minute, and that we are in greater danger while driving to the airport. Likewise, seeing some lucky winner of the lottery makes people buy tickets, even when the odds of winning are almost zero. So, seeing a terrorist attack makes us overestimate the danger that it will happen to us.

Since terrorist attacks increase our perceptions of danger, they tend to make us less trusting in general. We tend to become more defensive and hardened in our opinions. Brene Brown, Ph.D. has suggested that the 9-11 attacks had the impact of polarizing our country. She said that our decreased feelings of safety made us more entrenched in our positions. And the division between Republicans and Democrats, conservatives and liberals is greater than I have seen in my lifetime.

So, what can we do? Of course, we must take the necessary steps to identify and prevent attacks when we can, and to fight the groups that carry them out. But, we also need to remind ourselves of the truth that terrorism has a much greater chance of changing our lives than it does of ending our lives.