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Bobby Fischer was playing chess at age 6. Mozart wrote his first symphony at 8. Could it be that Jack Welch was firing direct reports at 9?

There's a long-standing debate about whether leaders are born or made. But let's not revisit nature versus nurture. Instead, let's ask a weirder question: Could it be that your point of view on this issue is what actually makes you a better or worse leader? And if so, is nature or nurture the more career-enhancing POV?

This psychological puzzle starts with the research of Stanford's Carol Dweck. Her latest book, Mind-set: The New Psychology of Success, should be on every business manager's bookshelf. Dweck has found that individuals succeed or fail based on how they think about intelligence. She says people have one of two mind-sets on the matter.

People with a fixed mind-set believe that intelligence is static. Your behavior provides a sample of your true underlying intelligence, like a taster spoon from a tub of ice cream. And because people will judge your intelligence by the samples you provide, you'll definitely scoop out an Oreo chunk whenever you have the chance. The consequence: You'll avoid challenges. (If you fail, others will see that as a taste of your true ability.) You'll be threatened by negative feedback. (Isn't your critic just claiming to be smarter than you?) You'll exert less effort. (Really smart people don't need to try hard.)

The second group, Dweck says, are those with a growth mind-set. These people believe intelligence can be developed, like muscles. If you're in this camp, her research shows, you'll test yourself more, despite the risk. (After all, if you try to bench-press more weight and fail, no one will mock you as a "born weakling.") You're more inclined to accept criticism--ultimately, it makes you better. You perceive hard work as the path to mastery, not as a sign of insufficient genius.

Tiger Woods is an athlete with a growth mind-set, someone who obsesses about his game and makes incremental improvements. Manny Ramirez of the Boston Red Sox appears to have a fixed mind-set, relying on his enormous natural gifts to succeed (but not as keen on things like attending spring training). All of us blend the mind-sets in our heads. We might say, "I can't draw." But few of us would say, "I was born without the ability to ride a bike."

Now the puzzle deepens: Dweck has begun to explore whether we can intervene and change people's mind-sets, and if so, will that make them more successful? Earlier this year, Dweck and two colleagues, Kali Trzesniewsi of Stanford and Lisa S. Blackwell of Columbia, ran an experiment on junior high schoolers. If they trained the students to have a growth mind-set, would the kids' math grades improve? In less than two hours over eight weeks, they taught the students concepts such as: Your brain is like a muscle that can be developed with exercise; just as a baby gets smarter as it learns, so can you; everything is hard before it gets easy--never give up because you don't master something immediately.

The results were astonishing. The brain-is-a-muscle students significantly outperformed their peers in math, many showing dramatic turnarounds, such as the student who went from a failing grade to an 84 on her next exam. Dweck's work shows that a pure idea intervention can have a substantial effect. "The brain is a muscle" is an idea that stuck.