When you self publish, you self advertise and you keep track of sales and slumps.
It's nice when Kindle and Amazon alert you to royalties. And while mine have been small, each month something has come in.
So when I release a book, and it just sits there... I get depressed.
I worry, did I not plug it enough? Has the reading public gotten sick of me already? Don't they want to know the rest of the story?
It's a waiting game.