Earlier quoted context omitted.
I disagree. This is the case for anything entrepreneurial. Vast majority of ventures fail. Reward/Risk ratio (in finance we call it Sharpe ratio) generally equalises across the spectrum. That is there is no free lunch. You can choose an activity that has better odds of making money. But you will make leas money on average.
I think you underestimate the cost of writing a well-researched book. Pre-publication, the process consumes lots of time and energy and money while generating zero revenue, output, or other benefit. Very different from most business ventures. Source: I have written a book, and have also started my own business and have worked for many startups. (VC-backed startups pay their employees.)
Being a paid employee of a start-up is different. That would be similar to receiving an advance from a publisher to write a book.