To cope, they emotionally armor up. Many of the cops I was around developed a cynical, dehumanizing and hard-edged sense of humor that was an attempt to insulate themselves from the pain of seeing a dead child or the extinguished life of a young girl they arrived too late to save.

Many of us see cops as relatively invulnerable as they patrol the streets. The cops themselves do not perceive their situation that way. As criminologist George Kelling wrote in City Journal in 1993, “It is a common myth that police officers approach conflicts with a feeling of power — after all, they are armed, they represent the state, they are specially trained and backed by an ‘army.’ In reality, an officer’s gun is almost always a liability ... because a suspect may grab it in a scuffle. Officers are usually at a disadvantage because they have to intervene in unfamiliar terrain, on someone else’s territory. They worry that bystanders might become involved, either by helping somebody the officer has to confront or, after the fact, by second-guessing an officer’s conduct.”

Even though most situations are not dangerous, danger is always an out-of-the-blue possibility, often in the back of the mind.

In many places, a self-supporting and insular police culture develops: In this culture no one understands police work except fellow officers; the training in the academy is useless; to do the job you’ve got to bend the rules and understand the law of the jungle; the world is divided into two sorts of people — cops and a — holes.

This is a life of both boredom and stress. Life expectancy for cops is lower than for the general population. Cops suffer disproportionately from peptic ulcers, back disorders and heart disease. In one study, suicide rates were three times higher among cops than among other municipal workers. Other studies have found that somewhere between 7 percent and 19 percent of cops suffer from post-traumatic stress disorder. The effect is especially harsh on those who have been involved in shootings. Two-thirds of the officers who have been involved in shootings suffer moderate or severe emotional problems. Seventy percent leave the police force within seven years of the incident.