One of the major aspects that helps set a successful author apart from the millions of published writers, is how they approach the marketing-beast. Many people spend months or even years writing a book, and as soon as they receive the "Congratulations, you are published!" message from Amazon, they pour a glass of wine and put their feet up.
Serious authors know that the slog begins not when you first decide to put pen to paper. It starts once your writing has been released in the wild. Yup. Your marketing efforts will determine how many people get to see your book. The more people are directed to your eBook on Amazon, the books you sell, the more $ you make.
The commitment required for successful marketing is long term, not a one-night stand.