Anders Ericsson wrote a paper in 1993 called The Role of Deliberate Practice in the Acquisition of Expert Performance. This was the evidence that Gladwell quoted in his book to make his “10,000-hour rule.” However, Ericsson has since said that Gladwell was wrong to use the number as it was just an average of the students Ericsson was testing, not a magic number. Ericsson did the research, Gladwell wrote about it, Ericsson wrote a rebuttal about how Gladwell was wrong, and Gladwell has defended his statements.
Ericsson’s research contained an average amount of time of practice around 10,000 hours for his most talented students. This included some who were below 10,000 as well as some who were above. Gladwell then interpreted that data to mean that 10,000 hours was a “magic number of greatness” with no “naturals” or “grinds” (39-41).
Ericsson then published a rebuttal named The Dangers of Delegating Education to Journalists and said that Gladwell was wrong. A BBC article quotes Ericsson as writing “The 10,000-hour rule was invented by Malcolm Gladwell… Gladwell cited our research on expert musicians as a stimulus for his provocative generalisation to a magical number” (BBC). This was Ericsson saying explicitly that Gladwell got carried away in creating his rule. Ericsson also goes on to say that his research was about meaningful or “deliberate” practice, yet Gladwell never mentioned it in Outliers.
Gladwell later said that the reason behind Ericsson disagreeing with him is because Gladwell believes more in natural talent, but as a reminder, Gladwell did not mention any effects of genes or innate ability on skill and cited that there were no fast or slow learners. This doesn’t seem to support that the difference is his belief in natural talent, but it is his defense.