FAIRBANKS — Why did Major Nidal Malik Hasan, a psychiatrist, go on a shooting rampage at Fort Hood, killing 13 people and wounding more than 40 people. Some are still in the hospital in intensive care.

Major Hassan has been called “crazed,” “crazy” and “paranoid.” Some say he “snapped” because of anti-Muslim prejudice. Was he mentally ill or was something else in his mind?

His behavior was bizarre even before the killings. In an environmental health class Hasan took at the University of Health Sciences at Bethesda Maryland, for example, the students were supposed to give presentations on topics like mold, soil, and water contamination.

Hassan, however, ignored the assignment and got up before the class and began to speak on an entirely different topic, “Is the war on terror a war on Islam.”

When he was challenged on his views, Hasan became visibly upset. He became sweaty, he was emotional,” his classmate Lt. Col. Val Finnell told Fox News.

We in the West have difficulty fighting terrorism because we do not understand the psychology of our enemies. Why would anyone throw away his life, whether Hassan who must have doubted he could emerge alive, or the terrorists of 9/11?

Another psychiatrist, Paul McHugh, offers an explanation in his book “The Mind Has Mountains,” which makes the psychology of terrorism — almost — understandable.

Terrorists like Hasan are in the grip of an “overvalued idea.” Someone in the grip of an “overvalued idea” takes an idea shared by others in his culture but transforms it into a monomania. The person will sacrifice anything — family, fellow feeling, health, even life itself––in the service of this all-consuming passion.

An overvalued idea is not the same thing as a delusion. A delusion is a false idea such as “The CIA put a radio transmitter in my brain.” Overvalued ideas, in contrast, develop from assumptions that are widely shared in the culture, like good-looking women are very thin or, in Hasan’s cultural circles, his extremely radical jihadist views.

Fanatics in the grip of an overvalued idea do not try to fight it.

Quite the contrary, they cherish the idea, savor it, nurture it and defend it relentlessly. This is just what Hasan did — talking again and again about his jihadist beliefs and defending them emotionally, voicing his objections to Muslims fighting the war on terror to people in his mosque, and reaching out to people associated with Al Qaeda.

The “overvalued idea” is not actually so strange. Americans are quite familiar with one such overvalued idea, the condition “anorexia nervosa” or nervous

refusal to eat.

An anorexic young woman is not delusional or crazy. Many people around her agree that thinness is an attractive healthy ideal,” McHugh points out. But the anorexic overvalues this idea. The quest for thinness turns into a monomania. At the extreme, some anorexic young women will sacrifice anything in the quest for thinness, ruining their own health and even causing their own death.

“Patients suffering from this illness take an idea common among young women in our society — thinner is better — and amplify it into a commitment so dominant that they starve themselves,” writes McHugh.

If we think of terrorists like Hassan as having a disorder of the mind similar to anorexics we can perhaps understand the mindset we are up against. The overvalued idea driving terrorists is that America is the “great Satan,” the enemy of Islam, an evil godless culture that must be destroyed.

The greatest danger to us lies in our own difficulty in taking this idea seriously because to us it seems so “crazy,” as does going on a shooting spree against unarmed soldiers as did Hasan.

But read Hasan’s words and take them seriously. He gave a powerpoint presentation to his supervisors and two dozen mental health staff members on Islam, rather than the medical topic he was supposed to be talking about.

His last bullet point in a slide titled comments read clearly. “We love death more then (sic) you love life.”

These are not empty words. These are words that resulted in the Ft. Hood massacre.

Judith Kleinfeld is a professor of psychology at the University of Alaska Fairbanks. She welcomes comments or criticism. E-mail: ffjsk@uaf.edu.