What one thing can determine whether or not you're successful in life?

Dozens of studies show that willpower is the single most important keystone habit for individual success… Students who exerted high levels of willpower were more likely to earn higher grades in their classes and gain admission into more selective schools. They had fewer absences and spent less time watching television and more hours on homework. "Highly self-disciplined adolescents outperformed their more impulsive peers on every academic-performance variable," the researchers wrote. "Self-discipline predicted academic performance more robustly than did IQ. Self-discipline also predicted which students would improve their grades over the course of the school year, whereas IQ did not.… Self-discipline has a bigger effect on academic performance than does intellectual talent." [The Power of Habit]

Measured concurrently, emotionally stable and conscientious participants reported higher incomes and job satisfaction. [Barking Up the Wrong Tree]

…the personality traits Conscientiousness and Neuroticism have a strong impact on the instantaneous probability of finding a job, where the former has a positive effect and the latter has a negative effect. [Barking Up the Wrong Tree]

…our findings suggest that conscientiousness is the trait most broadly associated with marital satisfaction in this sample of long-wed couples.[Barking Up the Wrong Tree]

Among adults over age 45 (n = 2,419), Neuroticism and low Agreeableness were associated with metabolic syndrome, whereas high Conscientiousness was protective. Individuals who scored in the top 10 percent on Conscientiousness were approximately 40 percent less likely to have metabolic syndrome… [Barking Up the Wrong Tree]

Conscientiousness, which was the best predictor of longevity when measured in childhood, also turned out to be the best personality predictor of long life when measured in adulthood. [Barking Up the Wrong Tree]

…conscientiousness was the trait that best predicted workplace success. What intrigues Roberts about conscientiousness is that it predicts so many outcomes that go far beyond the workplace. People high in conscientiousness get better grades in school and college; they commit fewer crimes; and they stay married longer. They live longer – and not just because they smoke and drink less. They have fewer strokes, lower blood pressure, and a lower incidence of Alzheimer's disease. [How Children Succeed: Grit, Curiosity, and the Hidden Power of Character]

Those in the fitness program got fitter; those working on study discipline got more schoolwork done; the people in the money-management program saved more money. But — and here was a truly pleasant surprise — they also got better at other things. The students who did the study-discipline program reported doing physical workouts a bit more often and cutting down on impulsive spending. Those in the fitness and money-management programs said they studied more diligently. Exercising self-control in one area seemed to improve all areas of life.[Willpower: Resdiscovering the Greatest Human Strength]

When your willpower levels have been drained by an earlier test, that's when you're most vulnerable to temptation. One way to protect yourself is to form so-called 'if-then' plans… willpower depletion had no such adverse effect on students who followed the additional, more detailed plan: '…And if I have solved one anagram, then I will immediately start work on the next!'. [BPS Research Digest]

How can you use precommitment to keep yourself from giving in to unwanted desires? You're probably already doing so — for example, by asking your significant other, on the way to a restaurant, not to let you order dessert when you get there. Dan Ariely, that tireless student of human irrationality, has collected several interesting precommitment anecdotes from regular people, including one who placed her credit card in a container of water in the freezer, thereby requiring a cooling off — er, that is, warming up — period before use, and another who, before a date with a guy she knew she shouldn't sleep with, wore her "granniest" underwear — presumably to deter herself from disrobing… [We Have Met the Enemy]

All the children in a class were told to skip breakfast one morning, and then, by random assignment, half of the children were given a good breakfast at school. The others got nothing. During the first part of the morning, the children who got breakfast learned more and misbehaved less (as judged by monitors who didn't know which children had eaten). Then, after all the students were given a healthy snack in the middle of the morning, the differences disappeared as if by magic. [Willpower: Resdiscovering the Greatest Human Strength]

…the more total self-control, the better the relationship fared. Multiple benefits were found for having mutually high self-control, including relationship satisfaction, forgiveness, secure attachment, accommodation, healthy and committed styles of loving, smooth daily interactions, absence of conflict, and absence of feeling rejected. [Barking Up the Wrong Tree]

…self-control is not selfish. Willpower enables us to get along with others and override impulses that are based on personal short-term interests. It's the same lesson that Navy SEAL commandos learn during a modern version of Stanley's ordeals: the famous Hell Week test of continual running, swimming, crawling, and shivering that they must endure on less than five hours' sleep. At least three-quarters of the men in each SEAL class typically fail to complete training, and the survivors aren't necessarily the ones with the most muscles, according to Eric Greitens, a SEAL officer. In recalling the fellow survivors of his Hell Week, he points out their one common quality: "They had the ability to step outside of their own pain, put aside their own fear, and ask: How can I help the guy next to me? They had more than the 'fist' of courage and physical strength. They also had a heart large enough to think about others." [Willpower: Resdiscovering the Greatest Human Strength]