Author Michael Lewis spoke about his daughter’s death in a car crash in an interview on Andrew Sullivan’s podcast.

Dixie Lewis, the 19-year-old daughter of Moneyball and The Fifth Risk author Lewis and his wife, photographer Tabitha Soren, died in late May after a car driven by her boyfriend crashed into a truck.

Michael Lewis told Sullivan that the cause of the accident remains a mystery, the Independent reports.

“Nobody was drunk, no one knows why they crossed a yellow line and went straight into a truck,” Lewis said.

Lewis described the grief that he, Soren, and their two other children felt as “exhausting.”

“I’ve been asking myself why do I feel so depleted, and I think it’s because I think your mind maps a kind of reality at any given time, and you kind of have an imagined future and that child is in that future,” he said. “Your mind is already working to prepare you for the death of your parents, and from a very early age you kind of think that will happen. And when it happens, it will be sad, but you kind of prepared yourself for it. Your mind does not prepare you for the death of a child.”

Lewis’ most recent book, The Premonition: A Pandemic Story, was published on May 4.

Michael Schaub is a Texas-based journalist and regular contributor to NPR.