Every year, close to 1 million people around the world kill themselves.

Florida State University Bright-Burton Professor of Psychology Thomas Joiner has spent much of his career trying to find out why. After all, lots of people are hopeless and depressed, many severely. Why do some people choose to end their own lives and others don't? The answer, he believes, could save lives.

"There's an idea that suicide is a mode of death that stands apart from others, but there are clear reasons why people die by suicide," said Joiner, an internationally recognized suicide expert. "Just like heart disease, if you understand it, you can prevent it." In a groundbreaking theory outlined in his new book, "Why People Die By Suicide" (Harvard University Press), Joiner says that those who kill themselves not only want to die, they have learned to overcome the instinct for self-preservation. The desire for death, according to Joiner, is composed of two psychological states: a perception of being a burden to others and a feeling of not belonging. Alone, neither of these states is enough to instill the desire for death, but together they produce a desire that can be deadly when combined with the acquired ability to enact self-injury.

So how does one overcome the natural instinct for self-preservation? In a word: Practice. In Joiner's theory, suicide victims literally "work up" to the act by getting used to danger, fear and pain. They may do this in a variety of ways over their lifetime.

For some this practice is deliberate. They engage in reckless behavior, cut or otherwise hurt themselves or have repeated suicide attempts. Others may have a history of accidents or medical procedures while still others become inured vicariously. Perhaps like physicians—who have an elevated risk of suicide—they are exposed through their work to pain and suffering on a daily basis. Eventually, self-injury and dangerous situations become unthreatening and mundane, according to Joiner, making suicide easier to carry out.

"Some people think that those who commit suicide are weak," he said. "It's actually about fearlessness. You cannot do it unless you are fearless, and this is behavior that is learned."

Joiner's theory explains why seemingly disparate groups of people, such as anorexics, athletes, prostitutes and physicians, have higher than normal rates of suicide. The lifestyles of all of these people expose them to pain—either that of their own or others—and in a sense harden them against suffering, Joiner said.

It also explains why a relatively large number of people want to kill themselves but only a fraction do. Likewise, many people are capable of killing themselves but most do not. There are relatively few people in the dangerous convergence zone of desire and capacity for suicide, according to Joiner, and these are the people who are at greatest risk for serious suicidal behavior.

But knowing the risk factors makes prevention possible, Joiner said, noting that maintaining good interpersonal relationships is essential. This is perhaps the downfall of many older white men—the demographic that has the highest suicide rates of all. "If you think you belong or that you are contributing, you are going to be protected from suicide no matter what else is going on," he said.

Scare campaigns such as those that are sometimes targeted at teenagers do not work as prevention tools and may, in fact, backfire because they further habituate the at-risk patient to the idea of suicide. Joiner noted that rock singer Kurt Cobain repeatedly watched news footage of a government official who committed suicide during a news conference before carrying out his own suicide in 1994.

While Joiner's book is based on his own experience as a clinical psychologist as well as studies that he and other researchers have conducted, the book is also personal. Joiner was a graduate student when his father took his own life—an event that came as a shock to his family and friends. But Joiner now understands why it happened, and that's information that he wants to share with the 2,500 other families who learn the news of a loved one's suicide every day.

Perhaps, he said, one day that number will be less.