Many of my career mentors have given me a similar tidbit of advice: Do what you know.
For the most part, it seems wise. I personally couldn’t imagine being in a job I knew absolutely nothing about. How long would it take for me to be successful? Would I get on my colleagues' nerves having to constantly ask for assistance?
But if you asked billionaire Richard Branson, it’s the worst advice he’s ever received. He broke through by doing the complete opposite.
“Most of my successful businesses were in industries where I had no industry experience at all,” Branson said on a recent episode of the Work Life with Adam Grant podcast. 
Exploring new projects and fields is smart, said Grant, a Wharton organizational psychologist: People who stay in a single, familiar industry sometimes develop “cognitive entrenchment,” he said.
In other words, as employees and scholars gain expertise, they can lose “flexibility with regard to problem-solving, adaption and creative idea generation,” according to research from Rice University published in 2010.
Instead, “when you’re fresh to an industry, from the outside, you get that ability to see what’s taken for granted and challenge it,” Grant told Branson on the episode.
I find Branson’s perspective insightful — after all, you can’t learn something new without trying something new.

CNBC