I just finished Side Hustle – From Idea to Income in 27 Days (Chris Guillebeau, 2017, 272 pages). Although the title for this book sounds very appealing, the content is a less interesting than one could expect.
However, if you want more rigor than just following some few examples of people that made things happen, then it may just not work.
The problem with books like this one is that a few inspiring examples and some generic advice is not good enough to show you how to really do something. It can be helpful to some, but it may also be misguiding to those trying to comprehend the chances and not only the rosy side of a few good examples.
As an example of interesting questions that go unanswered: what are the percentage of people who try building a side business? How many of those report success? How long the process take on average? What profiles or fields of operation are over-represented between those who managed? What are the evidences backing up any of these more generic claims?
In any case, once you know this is one of those books with simple encouraging steps and superficial justification, then it’s up to you if it can be useful or not.