Amos and I shared the wonder of together owning a goose that could lay golden eggs – a joint mind that was better than our separate minds. … Some of the greatest joys of our collaboration-and probably much of its success – came from our ability to elaborate each other's nascent thoughts: if I expressed a half-formed idea, I knew that Amos would be there to understand it, probably more clearly than I did, and that if it had merit he would see it. Like most people, I am somewhat cautious about exposing tentative thoughts to others – I must first make sure that they are not idiotic. In the best years of the collaboration, this caution was completely absent.

My training took seven years. I didn’t learn how to make sushi for the first three years. I only got two days off a month, and slept on the restaurant floor. But I loved the job. I’d go to the fish market every morning. I got to open the restaurant and see the customers. I’d watch my mentor making sushi and would copy him under the table, practising with my fingers.

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.

The friends with whom I sat on graduation day have been my friends for life. They are my children’s godparents, the people to whom I’ve been able to turn in times of trouble, people who have been kind enough not to sue me when I took their names for Death Eaters.

But I'm ready for what's next after rugby. Being able to not just say that, but to truly feel it, is a privilege. Ultimately, getting to leave your sport on your own terms is all you can really hope for as an athlete.