If I may take artistic license to reinterpret the comment, what I get from the comment is that given the very short term nature of the sales, no one really had

If I may take artistic license to reinterpret the comment, what I get from the comment is that given the very short term nature of the sales, no one really had time to read the content and then publicize their opinions to yield this sales curve. Basically, there is no word-of-mouth or social proof effect evident in this sales curve. Indeed, we see the opposite - more people bought the book before others subsequently purchased it. Sales were due to pent up demand versus waiting for others to verify quality or value. Basically, the moment it was offered for sale, the product was purchased practically sight unseen (altho the article mentions that he in effect pre-released portions of the text to his newsletter subscribers). Given this, the book could have been low quality and it wouldn't have impacted this sales curve. In which case, the OP could have spent 5 minutes, 5 hours, 5 days, or 5 months writing the book and the sales curve would look similar. What I gleaned from this article was not that it took substantial effort to write a book to evoke this sort of sales curve, but rather there was a process of building expectation and an audience which would result in substantial sales for a book, regardless of its level of quality. The level of quality became assumed and did not require prior evidence. Thus, labor / effort in writing was not proportional to sales.