But I need to show my work during the process. In the editing room, very often I invite friends and I do some test screenings with friends or people I know: editors, journalists sometimes. I ask them, Is it boring? Is it too long? What do you think?

MOVE was very supportive through all of that. My wife had a natural childbirth — MOVE coached us through a lot of that.

I have had students and postdocs of the first class close to four hundred people.

Satya is very good at extracting the maximum value from my time and making sure I look at all the important things. He’s very thoughtful, good at working with people, working through problems in a calm sort of way.

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.

So given a Time Turner, I would tell my 21-year-old self that personal happiness lies in knowing that life is not a check-list of acquisition or achievement. Your qualifications, your CV, are not your life, though you will meet many people of my age and older who confuse the two. Life is difficult, and complicated, and beyond anyone’s total control, and the humility to know that will enable you to survive its vicissitudes.

I cannot possibly reveal the full horror of my most embarrassing moment, but it took place in a pub in Exeter (which is a town in the south coast of England, where I went to university) in 1984 and involved a joke made by me that backfired spectacularly. The whole debacle was witnessed by my friend Pauline, who is mentioned elsewhere on this fansite (I have to keep her happy in case she TELLS).

As the screenwriter, the majority of my input comes at an earlier stage.

So why do I talk about the benefits of failure? Simply because failure meant a stripping away of the inessential. I stopped pretending to myself that I was anything other than what I was, and began to direct all my energy into finishing the only work that mattered to me. Had I really succeeded at anything else, I might never have found the determination to succeed in the one arena I believed I truly belonged. I was set free, because my greatest fear had been realised, and I was still alive, and I still had a daughter whom I adored, and I had an old typewriter and a big idea. And so rock bottom became the solid foundation on which I rebuilt my life.

I can remember feeling elated after writing the first Quidditch match, which flowed out of the pen and was barely revised afterwards.