I think you're referring to the belief that it takes 10,000 hours of practice in order to "become a world class expert in anything." This "10,000 hour rule" was

I think you're referring to the belief that it takes 10,000 hours of practice in order to "become a world class expert in anything." This "10,000 hour rule" was made famous by the book Outliers and is primarily based on the research of K. Anders Ericsson. 10,000 hours of practice is often equated to 10 years, though I'm not sure if the book explicitly makes this parallel.