That's phenomenal! I agree that building an audience is the hardest part and it's what traditional publishers bring to the table for most people. Just last week I saw someone self-publish some artwork in an area they have an audience and they made $4000 in a day. The only marketing they did was a single tweet. I don't think most individuals would be able to gain this level of authority without years of work and spending lots of money traveling to and speaking at conferences and writing blog posts or publishing videos.