I can attest that this article is right, not just from my very recent experience but also from many who share their woes in writing groups and online. Beware grasshopper, even if you publish via a known publisher you do all the marketing. Some authors I trust told me that for the small of amount of books the first book of my series, The Sylph's Tale, sold they are amazed at the comments on Amazon, only one is by an honest author who read the book. Don't rely on family nor friends; they will not be your fans. Social media is the king of sales.
Note: The Sylph's Tale, available at Draft2Digital: https://www.books2read.com/u/mBM76N
Book Two, VIRGINS to be published May 2018