In Outliers, Gladwell examines the factors that contribute to high levels of success. To support his thesis, he examines the causes of why the majority of Canadian ice hockey players are born in the first few months of the calendar year, how Microsoft co-founder Bill Gates achieved his extreme wealth, and how two people with exceptional intelligence, Christopher Langan and J. Robert Oppenheimer, end up with such vastly different fortunes. Throughout the publication, Gladwell repeatedly mentions the "10,000-Hour Rule," claiming that the key to success in any field is, to a large extent, a matter of practicing a specific task for a total of around 10,000 hours.