I think that really depends on how carefully you prepare and plan your strategy. Just writing a book and publishing it on Kindle will most likely get you nowhere.
Authors who are successful at Kindle self-publishing put months and months of work into devising, testing and revising a comprehensive promotional strategy - and they frequently put hundreds or even thousands of dollars into marketing their work.
At the outset, you should clearly define your market - the age group and interests of your intended readership. Your promo strategy will be based on that and laser-focussed to create a buzz around your book within that demographic.
Success on Kindle requires the following:
1. A very well crafted book, carefully tailored to a clearly defined market.
2. A clear, comprehensive marketing strategy.
3. A lot of time and effort.
4. Money to spend on professional marketing.
That's the truth. Anything else is just a pipe-dream.