Theo Epstein, president of baseball operations for the Chicago Cubs, became one of the most important people in Major League Baseball by following a rule that fast-tracked his career.
It set him up to achieve what many thought was impossible, a resurrection of the Chicago Cubs. After 108 years, the team won the World Series again in 2016.
"Whoever your boss is, or your bosses are, they have 20 percent of their job that they just don't like," Epstein tells David Axelrod on his podcast, "The Axe Files."
"So if you can ask them or figure out what that 20 percent is, and figure out a way to do it for them, you'll make them really happy, improve their quality of life and their work experience."
In other words, take on the aspects of your boss' job that he or she hates.
By diving into the less glamorous work, you will gain respect as well as "invaluable experience for yourself," Epstein says.
The sports titan says that idea was crucial to his success with the San Diego Padres from 1995 to 2002, where he rose to become director of baseball operations. He took every opportunity to learn from Kevin Towers, who was the general manager of the team.
Epstein reportedly put in 70 hour work weeks, while also getting his J.D. at the University of San Diego School of Law.
Epstein was then named the assistant general manager of the Boston Red Sox. At 28, he became general manager. At the time, he was the youngest GM in history. He helped the team win its first World Series title in 86 years.
The Chicago Cubs executive still swears by the 20 percent rule.
"If you do a good job with it, they'll start to give you more and more responsibility," he says.
More From CNBC