In economics class they teach us stuff like opportunity cost. Opportunity cost is the cost of an activity measured in the amount of money you could be making if you did something else.
So for example if you in college the cost of going to college isn't just the tuition its also the 40 or 50k that you could have been making had you not gone to college and worked, so even if you get a scholarship your still technically losing money (although, of course, you make it up in increased wages later on).
So lets say he could have gotten a 60k job being a journalist (I don't actually know how much they make) and he spend 6 months full time writing this book. Therefore he would have to sell 15,000 books just to break even.
And btw in most parts of the business world a 5% margin is atrocious, that is considered absolutely paper thin. About the only people that come anywhere near that margin is a bulk store like costco. My family owns a sports nutrition store and have lower prices than everyone around us but we have had to start cutting out and negotiating with distributors for any products that have lower than a 45% margin. The thing is we have so many fixed costs like marketing, rent, labor, franchise fees, etc that we need high margins.
