Malcolm Gladwell. Amy Sussman/Getty Images The 10,000 Hour Rule — closely associated with pop psych writer Malcolm Gladwell — may not be much of a rule at all.

The principle holds that 10,000 hours of "deliberate practice" are needed to become world-class in any field.

When psychologists talk about deliberate practice, they mean practicing in a way that pushes your skill set as much as possible.

In "Outliers," Gladwell contends that early access to getting 10,000 hours of practice allowed the Beatles to become the greatest band in history (thanks to playing all-night shows in Hamburg) and Bill Gates to become one of the richest dudes around (thanks to using a computer since his teen years).

But a new Princeton study tears that theory down. In a meta-analysis of 88 studies on deliberate practice, the researchers found that practice accounted for just a 12% difference in performance in various domains.

What's really surprising is how much it depends on the domain:

• In games, practice made for a 26% difference

• In music, it was a 21% difference

• In sports, an 18% difference

• In education, a 4% difference

• In professions, just a 1% difference

The best explanation of the domain dependency is probably found in Frans Johansson's book "The Click Moment."

In it, Johansson argues that deliberate practice is only a predictor of success in fields that have super stable structures. For example, in tennis, chess, and classical music, the rules never change, so you can study up to become the best.

But in less stable fields, like entrepreneurship and rock and roll, rules can go out the window:

• Richard Branson started in the the record business but quickly branched out into fields well beyond music: Virgin Group has 400 companies and is launching people into space.

• Then there's a band like the Sex Pistols, who took the world by storm even though Sid Vicious could barely play his bass.

So mastery is more than a matter of practice.

"There is no doubt that deliberate practice is important, from both a statistical and a theoretical perspective. It is just less important than has been argued," the study's lead author, Brooke Macnamara, said in a statement. "For scientists, the important question now is, what else matters?"