No. We have a lot of customers, and we have a lot of research into our installed base. We also watch industry trends pretty carefully. But in the end, for something this complicated, it's really hard to design products by focus groups. A lot of times, people don't know what they want until you show it to them.

The second thing there was another thing I learned at Sequoia is that the culture of a business is built in the first six months by the first ten to 15 employees. These are magical, really, really important times. And I used to hear a lot even at Sequoia, a lot of entrepreneurs saying, “Hey, I'm too busy to think about culture. When we become a unicorn, when we grow, I'll worry about culture.” And for whoever has kids, it's almost like saying I'm too busy about educating my kids. When they turn 18, then I'll figure it out. Too late.

Don’t romanticise your “vocation”. You can either write good sentences or you can’t. There is no “writer’s lifestyle”. All that matters is what you leave on the page.

I think it's something that nobody's really talked about in the past because we're supposed to be this big, macho, strong person that has no weaknesses. You know, we're supposed to be perfect.

I try to start work before 9am. My writing room is probably my favourite place in the world. It’s in the garden, about a minute’s walk from the house.

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

I couldn’t have asked for better collaborators on the stage play than John Tiffany (director) and Jack Thorne (writer).

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

Even though I have a highly visual imagination, I’ve had to learn just how much can be said onscreen without a word, and David and Steve have taught me that.

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.