Talent = 10,000 Hours + Luck

It takes about 10000 hours to become an expert in something (Malcolm Gladwell).
This is approximately 1000 human days (discounting sleep, toilet breaks and other non working hours), which is approximately 3 years, which is equivalent
to the time taken by a student to complete his PhD. This means that at the end of the PhD, a student should be better than his supervisor because he or she spent almost 10,000 hours just studying his or her research topic, whereas the supervisor had to manage many other things + students during that time period.