The 10,000 hour rule suggests that expert performance is largely the result of time spent in deliberate practice, or “engagement in structured activities created specifically to improve performance.” In a study by Macnamara et al. (2014), it was discovered that only 20% of expert sport performance could be attributed to time spent deliberately practicing the sport.
A frequently referenced article by Ericsson et al. (1993) contends that high volumes of deliberate practice are required to attain expert performance. Ericsson and colleagues are not wrong; the statement they are making is likely a valid one. However, the authors also state that “experts carefully schedule deliberate practice and limit its duration to avoid exhaustion and burnout.” It's evident that this key aspect of their research is frequently overlooked or ignored. As the research by Macnamara et al. (2014) shows, deliberate practice is important; it's 1/5 of the puzzle. Just don't forget about the other 80%.
For more details about the study by Macnamara et al. (2014), you can read the paper here. You can find the Ericsson et al. (1993) paper here.
I touch on both of these papers in my research review on how early sport specialization impacts long-term athletic success, which you can view here.
Questions? Contact me on Twitter: @AdamVirgile