I get asked the same question. I did it by reading nearly every book in a medium-sized library over the course of a decade-and-a-half, and any other book anyone would give me or let me borrow. And then kept on reading after that.

I’ve probably read 15,000-20,000 books. At one point, I was reading 20-30 (full, adult) books a week. I did this for years. I’ve read seven books in a day.

It’s not possible for most, I know, but I did it.