Starting writing is stressful and scary and hard, but also, it's just like going to the gym. You're just stiff and weird, and you can't do it as well.

I had the experience of having my grandmother in a nursing home at the end of her life, and had dementia set in with my father. He was in a nursing home with dementia at the end of his life, but it happened for me personally 10 years ago. My father was much older than my mother, so I experienced it as a pretty young person. People's parents die at various ages, but my father died of mortality. He died of being an old person. Illness and stuff happened, but essentially, he was old and he was going to die.

In terms of my peer group, nobody's parents were dying of old age. There was no dialogue to have among friends. I had that experience, and then 10 years later, I started thinking about writing about it. It's obviously an indelible thing when that happens, and I wasn't looking for material at the time or anything; it just started becoming relevant to me.

I spent a lot of time on Diane Arbus film, not only writing it, but running around talking through various production issues. All this crud, and then it didn't happen. There's a lot of time-wasting stuff that happens in life with movies.

Producer Ed Pressman had a book about Diane Arbus - it's the only biography that exists - and there had been many Diane Arbus scripts. Many. I don't even know how many over the years. And it's sort of a cursed project, for lots of reasons. There's probably some pile somewhere of all these weird attempts, all these portraitures that can't get made.

Obviously, once you're finished, you're like, "Okay, I have to make this a movie now, and I need people - bodies to play these parts, and actors to bring this thing beyond a script." But when I was writing it, I wasn't thinking of actors; I was really thinking about creating three-dimensional characters.

Focus group was helpful in the way it always is when you make movies, especially with anything funny. You can find the right edit or the right beat. In terms of cutting and rhythm, I think it's essential to screen your movie before you lock picture.