How could Michael Jordan, born with once-in-a-generation athletic abilities, soar as one of basketball's greatest players of all time ... only to whiff his chance at a career in Major League Baseball?
Or why has William Shatner with his talent in the performing arts been acting successfully for over four decades in hits like Star Trekand "Boston Legal," but failed to launch a singing career?
In their new book "SuperFreakonomics," authors Steven Levitt and Stephen Dubner propose some answers.
"The fact is, if you look at anybody in the world who's really, really good at anything, the odds are that they were not so great at that when they were a little kid," Dubner said. "This whole idea of raw talent and genius are vastly overrated."
Born to be a great soccer player or a pianist? Not so, says Dubner. Sometimes something as simple as the month you were born can help make it possible for you to succeed.
Watch this story and more "SuperFreakonomics" on "20/20" Friday at 10 p.m. ET
"It's a bizarre, but very pronounced pattern, that if you look at, let's say, world class soccer teams, a lot of the guys on those teams were born in just a few months of the year -- turns out January, February and March. And very few of them are born, like, October, November, December," he said.
Dubner said this is not an astrological anomaly. Aquarians are not better soccer players than Sagittarians. Instead, the pattern exists because the cut-off age for youth soccer is Jan. 1 and being the oldest kid on your junior soccer team -- if only by a few months -- can actually determine your chance of becoming a professional soccer player.
"The older kids are bigger. They're a little more mature. They're a little faster," he said. "And then the coaches are looking for the best players. They select them and they keep doing this over and over, year after year."
"What's remarkable is that this effect, this relative age effect, lasts all the way up into the professional ranks," Dubner said. "That's what's really so astounding about it."
What Your Birthday Month Could Mean
The month you are born can also create devastating obstacles. For example, why should some pregnant women pray their baby is not born next May?
Babies born next May in places as far apart as southeastern Uganda and parts of Michigan, will be roughly 20 percent more likely to develop visual, hearing or learning disabilities than babies born in any other month next year, according to the SuperFreakonomics authors.
"It's a mystery until you figure out that those areas are where there's a very large Muslim population. And -- a lot of -- many Muslims, including a lot of pregnant women, fast during the month of Ramadan," Dubner told 20/20. "And if a pregnant Muslim woman fasts during Ramadan and with [the] first or second month of her pregnancy, there's a real chance that her child could have developmental difficulties."
This year Ramadan was from mid-August to mid-September.
It's an unintended consequence of an unexplored phenomenon.
"If you look at the right data with a different mindset, a new kind of question, you can shed light on -- on fundamental questions that have gone unanswered for thousands of years," said Levitt, the economist of the "SuperFreakonomics" duo.
Why Practice Makes Perfect
But the fundamental question on talent: are you born great or made great? The data reveals that whether you want to be a tennis champion, like Monica Seles, or a world class soprano like Renne Flemming, nothing determines our ability to succeed more than three simple words grandmothers have been telling us for centuries: practice makes perfect.
But not just any kind of practice will suffice. Dubner and Levitt said it has to be "deliberate practice."
"It says that if we set out to practice a particular thing in a given way that we will get a lot better at things," Dubner said.
In other words, you cannot be successful unless you practice frequently, with the desire and intention to get better; and with a coach or a teacher giving you feedback. That kind of practice made Seles a world tennis champion -- even though she had no tennis court to practice on for years.
"My dad just took a ... a simple string and put it between two cars in the parking lot in front of our high-rise building, and that's kind of where I started playing tennis," she said. "I played like that for almost two years and ... my fundamentals of the game were really learned out on a parking lot. So any time I talk to kids nowadays, I really tell them that no matter where you start playing, if you have the right fundamentals and you really work at it, I think good things can come."
Doctors: Better with Age?
Dubner said the data reinforces the values of the work-ethic: "When you get that good at something, you've worked at it in a way that other people haven't worked."
But it doesn't end there. Even after you have acquired a specialized skill, not practicing can have real negative consequences.
"It turns out that -- one of the few kinds of doctors who research suggests get better as they get older are surgeons. The reason seems to be is because they're getting constant feedback. Every time you operate you know pretty well and pretty fast how you did," Dubner said.
Dubner said that a skill like surgery differs from mammography, where technicians don't get quick feedback on their performance.
"It turns out that a lot of doctors [that perform mammograms] are never better than ... the day they left medical school," Dubner said.
While that statistic is not very reassuring for women getting mammograms, Dubner said it's informative for how doctors should be trained.
"The system couldn't be arranged to provide them with much better feedback about how they're doing. It just isn't the way that our current system operates," he said.
With a little more feedback and a lot more practice, according to "SuperFreakonomics," we can improve at anything we choose to do.
"A lot of us tell ourselves that we're not good at something. We tell ourselves, 'Well, I wasn't born to be good at it,' whereas you probably could become pretty good at it if you wanted to put in the hours," Dubner said. "So, really, I think the lesson here is that we overvalue raw talent a lot. And I think that's actually a kind of uplifting message."
CLICK HERE to read an excerpt from "SuperFreakonomics."