The jazz legend Charlie “Bird” Parker once told an interviewer that he put in at least 11 to 15 hours a day on his saxophone for more than three years. That is more than the 10,000 hours writer Malcolm Gladwell said are essential to become an expert in his popular book “Outliers.” But it took more than just practice
for Parker.

Scientists often look to chess to get an idea of the influence of practice, since the game has no physical restrictions but does have objective rankings that can be used to compare players.

By pooling the results of six studies with a total of roughly 1000 participants, a paper published in 2013 showed that “deliberate practice” only accounted for about 34 percent of the variance between chess players’ abilities.

This means that practice is essential, but not sufficient, for a person to master something. It can only partially explain why some people are grandmasters and others are not. Contrary to Gladwell’s hypothesis, plenty of the chess players accumulated more than 10,000 hours and didn’t receive more than an intermediate ranking, yet half of the masters in one study reached that skill level without spending nearly as much time.

But trying to put a number on the importance of practice may be missing the point.

Variance, the number that scientists are trying to use, has a strict mathematical definition but has a hazy meaning when it is applied to actual data. Variance helps determine the degree of correlation between one particular measurement and another. Outside of chess, it is much harder to find reasonable measurements of ability to correlate.

For example, the same paper that pooled data from chess studies did the same with music performances. The standards used to compare musicians in the various studies, including counting incorrectly played notes during a sight-reading test, could not be completely diagnostic, since there is always much more to music than reading what is on the page.

The results showed that about 30 percent of the players’ variance in ability could be attributed to deliberate practice. And there are plenty of other factors that make up that other 70 percent.

For example, there’s starting age. The best performers tend to start younger, which is still true when the study is controlled for total hours spent practicing. Additionally, a person’s current age matters. This is even the case for chess, a game in which players tend to peak in their late 30s, though it may be more obvious in other areas. After all, it’s not like a person is going to become an overnight pop sensation when he is 48 years old.

Intelligence also matters. In order to become an expert chess player, athlete or musician, a person should also be smart — unless that person is Derek Paravicini, the brilliant pianist who can’t count to three. 

At the end of the day, a person’s genes cannot be ignored — they definitely matter. Twin studies have revealed that even creativity, chess skills and musical ability are at least somewhat affected by a person’s DNA. This is even more true when a talent depends on physicality: No matter how much a person practices, he is not going to make it in the NBA if he is only 5-foot-3.

Not just anyone can be brilliant at everything, or, for that matter, anything. No one can predict from the outset who will be the next Charlie Parker, Mozart or Lady Gaga. Practice comes with no guarantees, and there is no magic number telling a person how much he will need. The only way to see what you are truly capable of is to give it your all.