But off the job -- watch out. Mr. Cusma, 36, rides one of the fastest motorcycles on the highway for 'an adrenaline boost, ' he says, adding: 'If you lose focus for one second, you crash and burn and die.' He also traveled to Russia to ride in a MiG fighter jet at more than 1, 000 miles per hour, soaring as high as 70, 000 feet. 'I don't want to wake up one day and realize I forgot to live my life, ' he says.

You might not think of yourself as a risk-taker. Think again. Recent studies using new experimental tools are upending the old belief that a person's appetite for risk is mostly inborn and unchanging. In fact, the reasons people take crazy gambles are far more complex. People who are cautious in some contexts may embrace risk in others, depending on factors such as their familiarity with the setting and their emotions at the time. The findings are exploding old stereotypes -- that women are innately more cautious than men, for example, or that teenagers are inevitably risk-seekers.

'It has been surprising to learn what a wide variety of reasons people have for risk-taking, ' says Elke Weber, a professor of international business at Columbia University and a leading researcher on risk. Understanding the roots of risk-taking can guide people in making better decisions, she says. Some long to advance in their careers or have new adventures but overestimate the hazards. Others race quickly and without thinking into dangerous risks.

Getting to know your surroundings can change how you size up a risk. 'Most people overestimate the probability of something going wrong' when they venture into unfamiliar turf, says Margie Warrell, a Melbourne, Australia-based authority on risk-taking who has coached many U.S. executives and employers. 'They also overestimate the consequences of things going badly, ' says Ms. Warrell, author of 'Stop Playing Safe.' With experience, they become more realistic, and learn they can handle the consequences of failure. 'The more often we step out of our comfort zone, the more we build our tolerance for risk-taking, ' she says.

Mr. Cusma is an athlete who practices martial arts and works out regularly, lending him confidence in handling physical risks. Adventures like taking the MiG flight, set up in 2009 through a Sarasota, Fla., travel company called Incredible Adventures, provide an emotional outlet, he says.

Sometimes an environment can shape risk-taking behavior. Jennifer Bellinghausen of Austin, Texas, a full-time caregiver to her disabled mother, isn't a risk-taker and never thought of getting a tattoo. The 39-year-old mother of two is terrified of needles and devotes her time to her family. But when she ventured into Mom's Tattoos in Austin several years ago with a friend who was getting one, the atmosphere in the shop changed her mind. Owner Deborah Obregon was so friendly that 'it was like we were instant best friends, ' Ms. Bellinghausen says. Ms. Obregon and another tattoo artist chatted with her for more than an hour, and Ms. Bellinghausen eventually took the plunge and got a 3-inch ankle tattoo of 'a little kitty cat, ' she says. 'It surprised me; I'm not a risk-taker, ' she says.

Strong emotions also spur risk-taking, research shows. Men who subscribe to a 'culture of honor' and believe they must defend their manhood or keep others from pushing them around are more likely to start an argument or attack a fellow motorist in a fit of road rage, says a 2012 study in Social Psychological and Personality Science. Other research shows that experiencing discrimination or rejection leads people to take more chances.

Ione Fletcher Kleven was annoyed one spring night in 2010 when she heard a fight break out in the front yard of her Castro Valley, Calif., home. She was determined to protect a garden she and her grandson had just planted there.

The 67-year-old portrait artist isn't usually a risk-taker. She dislikes flying, never gambles and has been married to her husband Oliver for 49 years. When she opened the door, her eyes met those of a helpless, screaming 14-year-old boy who was being beaten and stabbed by two burly men. 'I felt a rush of heat up my spine, ' says the 5-foot-6-inch grandmother, 'and I started running' straight toward the assailants. 'I got so mad I scared myself.'

She grabbed the boy's wrist and pulled him from under his attackers, screaming in their faces, 'Get out of here!' Her husband, a 6-foot former Marine, stepped onto the porch, and the attackers fled. The wounded teen recovered after surgery and several months' rehabilitation. Ms. Kleven is still surprised at the gamble she took, she says. 'I don't want to hurt anybody. But that night I would have ripped their heads off.'

Past studies typically measured people's appetite for risk by asking them to make choices in a laboratory setting between receiving a set amount of cash and playing a lottery with varying odds of winning different amounts of money. Men tended to make riskier choices in these experiments, which led researchers to conclude the women in general have less appetite for risk. The reality may have been that men typically are more used to taking financial risks.

Researchers have developed new tools to measure the nuances of risky behavior, and their findings have dashed that stereotype. A scale developed at Columbia University gauges risk-taking not only in the financial domain but in social, ethical, recreational and health areas. Researchers have found risk-takers in one realm may be timid in others.

Women feel more comfortable than men taking social risks, such as moving to a new city or wearing unconventional clothes, according to studies using this new, domain-specific risk-taking scale. When researchers factor in differences in how men and women perceive various kinds of risks, women are no more risk-averse than men, Dr. Weber says.

Another experimental tool, called the Columbia Card Task, enabled researchers to discover that teens aren't always the dangerous risk-takers they are believed to be. The task presents subjects with a computer image of several rows of cards face down. They earn money by turning over a winning card with a smiley face, but they lose a lot of money if they turn over a losing card with a frowning face. A 'cold version' of the task invites calm, rational decision-making by having participants decide all at once how many cards to turn over. A 'hot version' arouses more tension and emotion by requiring subjects to turn cards over one by one.

The task's creator, Bernd Figner, an assistant psychology professor at Radboud University in the Netherlands, likens the cold version of the test to making a single decision about car-insurance policies with varying deductibles and coverage limits. The hot version is like going out to a bar for a drink, then deciding with each new round whether to have another, he says. 'In the hot state, people are more likely to do risky things they will later regret.'

Teens take plenty of risks during the hot version of the task, Dr. Figner's research shows. But even a reckless teenager becomes sober as a judge during the cold version of the task in a laboratory. Helping teens understand how emotions can affect their choices -- for instance when they're feeling peer pressure or the pull of a strong temptation during a night out -- could help reduce risk-taking.