On September 11, 2001, I was enjoying the tail end of my summer holiday with family in Connecticut. Over the past year, I had been studying Osama bin Laden’s enigmatic fatwas as a graduate student at Oxford. At the time, al-Qaeda was not well known, so I was surprised to find that in the climate of paralyzing fear after the attacks, everyone around me professed to know exactly why this group had struck the United States.

A local soccer coach defiantly told me that practice was still on because keeping his team of eight-year olds cooped up indoors in fear is exactly what al-Qaeda secretly wanted. A cab driver told me he was going to keep taking customers from the train station because taking a few days off from work to grieve is exactly what al-Qaeda wanted.

But for the life of me, I couldn’t recall anything in bin Laden’s fatwas about playing soccer or driving cabs.

When President George W. Bush later responded by occupying Iraq in 2003, millions of Americans insisted that doing so was exactly what al Qaeda wanted. When, in 2004, Spain had the opposite reaction after the Madrid train bombings, and pulled back from that conflict, Americans told me that withdrawing from Iraq was actually what al-Qaeda wanted.

Today, a similar thing is happening with the Islamic State, also known as ISIS, as politicians and pundits accuse one another of “playing into the terrorists’ hands.”

How is everyone so savvy when it comes to knowing what terrorists want?

One explanation comes from a cognitive bias called correspondent inference theory. It was developed in the 1960s and 1970s by the social psychologist Edward Jones to explain the cognitive process by which an observer infers the motives of an actor.

The theory comes from the foundational work of Fritz Heider, the father of attributional theory. Heider saw individuals as “naïve psychologists” motivated by a practical concern – a need to simplify, comprehend, and predict the motives of others. Heider postulated that people process information by applying inferential rules that shape their response to behavior. In laboratory experiments, he found that we tend to attribute the behavior of others to inherent characteristics of their personality — or dispositions — rather than to external or situational factors.

Correspondent inference theory resolves a crucial question that Heider left unanswered: How does an observer infer the motives of an actor based on its behavior?

Jones showed that observers tend to interpret an actor’s objective in terms of the consequence of the action. He offered the following simple example to illustrate the observer’s assumption of similarity between the effect and objective of an actor: A boy notices his mother shut the door, and the room becomes less noisy; the correspondent inference is that she wanted quiet. The essential point is what Jones called the “attribute-effect linkage,” whereby the objectives of the actor are presumed to be encoded in the observable outcome of the behavior.

This is why soccer coaches, cab drivers, and everyone else in the world think they know what the terrorists want. People infer the motives of terrorists directly from the observable consequences of their violent behavior – not from studying the groups more scientifically.

This also helps explain why the presumed motives of terrorists seem to shift so rapidly and contradictorily. Consider that until the Paris attacks this past week, the conventional wisdom held that the group wields violence to achieve a Caliphate unadulterated by Western interference. Since the attacks, however, we’ve been told that actually the Islamic State wants to provoke the West into more military interference in order to showcase the West’s brutal behavior. Before the attacks, we were told that France is a juicy target for the Islamic State because of its failure to integrate its Muslim population. After the attacks, we are being told that the Islamic State actually wants France and the rest of the world to become even more xenophobic against Muslims on the theory that alienated moderates may be more receptive to extremism.

It’s no wonder the media are constantly talking up terrorists as “masterminds” who commit “sophisticated” attacks. Regardless of their outcome, whatever happens will invariably be seen as exactly what the terrorists want.

This post was updated at 1:15PM ET.