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.

Remember, if you sit at your desk for 15 or 20 years, every day, not ­counting weekends, it changes you. It just does. It may not improve your temper, but it fixes something else. It makes you more free.

Of all the gifts that tennis has given me over the years, the greatest, without a doubt, has been the people I've met along the way: my friends, my competitors, and most of all the fans who give the sport its life.

However, it was very natural that a failed surgeon with little experience in molecular biology had a hard time finding a position. A turning point came when I got a fax from Thomas Innerarity at the Gladstone Institute of Cardiovascular Diseases in San Francisco. After a short telephone conversation, Tom was brave enough to give me a postdoctoral position in his lab! Working at Gladstone was one of the best decisions I ever made in my life.

I moved to Argentina, then back to Tokyo and then to Anchorage, in Alaska, where I ran a restaurant. After 50 days the restaurant burnt down – an electrical fire. I lost my dream. I lost my money. I lost my passion. I thought about suicide, but thinking of my family and my kids made me realise I had to wake up.