What is one of the best or most worthwhile investments you have ever made — of money, time, or energy?

I think chess — actually, a number of things that I learned when I was young — it wasn't so much the chess itself; it was the skills that you were training while you were playing chess. So problem-solving, imagination, creative thinking, strategic thinking, all of these things — if you play chess to a high level, what you're really honing is those meta-skills. And I realized from quite young, that's one of the reasons I liked chess was this is a great practice for me to get good — sort of like a mental gym, if you like — to get really good at those other skills, which you could then translate to all sorts of other subjects like science or business.

We need to have mentors. I think I've always been pretty shameless about seeking out people much smarter and much more experienced than me from the very beginning. Michael Seibel and other people. And the more successful I got, the more leaders I started seeking out, whether it was investors, or Sheryl Sandberg at Facebook, or I got the opportunity to spend time with Warren Buffett and he became a close mentor of mine.

In Rakuten's case, adjustment certainly took time. At first, meetings often felt awkward. The first board meeting after the Englishization decision took four hours to complete – double the normal duration. But whenever executives asked if they could say certain things in Japanese, I told them no. I knew that the challenge would pay off – and it has.