I had a checklist in my mind of the things that make a biography practical. Is the source material centralized? Is it easy to find? Are there new primary sources that no one has ever had access to? Are all the sources in English? If they're not, are they in a language that you speak? And I realized that not only is Armstrong the most important figure of Jazz in the 20th Century, but he's a perfect subject for a biography for all of these reasons. I had always loved his music and I had been fascinated in him as a personality. And that's really the key to writing a biography.