In the real world, success can also be put down to developing and using three qualities — grit, cognitive abililty and physical ability.

These qualities came to the fore in a prospective, longitudinal study of more than 11,000 West Point cadets conducted by Duke University, and published in the Proceedings of the National Academy of Sciences. The research team discovered that both cognitive and non-cognitive factors can predict long-term achievement and success.

In addition, characteristics like intelligence, grit and physical capacity influence a person's ability to succeed in different ways. Grit is defined as putting one's passion and perseverance toward attaining important long-term personal goals.

University of Pennsylvania psychologist Angela Duckworth, who led the study, said grit is a key but often overlooked factor in success. Duckworth is also the Christopher H. Browne Distinguished Professor of Psychology in Penn's School of Arts and Sciences.

In 2007, Duckworth published a paper about grit in the Journal of Personality and Social Psychology. The study showed, for the first time, that grit is an important predictor of accomplishment. Duckworth has since continued collaborating with West Point in her continuing studies about success.

Every cadet enters West Point after an extensive, two-year process. He must also complete a brutal six-week initiation nicknamed Beast Barracks during the preceding summer classes. On average, three out of every 100 cadets quit during this training.

That these men gave up so quickly after such an arduous admission process intrigued Duckworth, and prompted her to study this group.

"I was looking for a context in which people might be quitting too early," she said. "There's such a thing as quitting at the right time. But there's also such a thing as quitting on a bad day when you're discouraged and maybe shouldn't be making such a big decision."

During the study, each student was evaluated on a grit score as measured by the 12-item Grit Scale created by Duckworth. This Grit Scale included entrance exams (SAT or ACT scores) and results from a battery of fitness tests each West Point hopeful must take before being admitted. These physical tests included a one-mile run, pull-ups and sit-ups, among others.

West Point provided data on whether cadets completed the Beast Barracks training and graduated from the academy. It also provided the cadet's GPAs for academic, military and physical performance.

Duckworth and her colleagues then ran a mega-analysis, incorporating all these data.

"We accumulated all this data in part so we could answer more definitively the question of whether grit predicted success outcomes," said Duckworth. "We now have more confidence in our original conclusions. At the same time, we wanted to explore where, perhaps, grit wasn't the most important factor."

Duckworth and her team also discovered that different personal characteristics predict different outcomes. They found that grit is crucial during Beast Barracks.

"The grittier you are, the less likely you are to drop out during that very discouraging time," she pointed out.

On the other hand, cognitive ability was the strongest predictor of academic grades during the four years of combined classroom time and physical training that followed Beast Barracks. Finally, grit and physical ability play a greater role than cognitive ability in determining who will graduate from West Point in four years versus who might drop out.

"This work shows us that grit is not the only determinant of success," according to Duckworth. "Yes, it's very important, helping people stick with things when they're hard, but it's not the best predictor of every aspect of success."

The findings add to the overall knowledge about what factors predict success. They also strengthen Duckworth's original theories about grit.

The findings, however, also highlight other attributes that are key to long-term achievement. "If you want to lead a happy, healthy, helpful life, you want to cultivate many aspects of your character, like honesty, kindness, generosity, curiosity," — and then there's grit.

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