You do not need a doctorate to be a successful online writer, all you need is to be an expert on a topic and write about it in a way everyone can understand what you have to teach.
If you ever read the book rich dad poor dad you see that the author explains to a woman that a doctorate in literature will not make her a best selling author, instead a course on selling will give her what she pursues, becoming a best selling author.
What is the difference between being a writer that writes good and a writer that sells good? A writer that writes well does not know what to write, he does not know what people are looking for, even though his books are very well written with the perfect writing style and no grammar errors.
However…
To become a best selling author the writer needs to understand what people want, what readers want, what search engines want, in order to rank high on search engines and to make people spend their hard earned money on his book.
I could write a deadly long article about that topic but instead I am going to give you links to books that will teach you from the best experts about selling.
Succeding at article writing is very tough, the best article writers write not once, not even one thousand articles, but tens of thousands of articles.
I always like to give a practical example, Sean R Mize, author of 24K+ articles and with more than 2 million views. This guy makes a six figure a year. Follow his advice, become a best selling author by writing as much as you can, then sell your book using the power of article marketing.