Back in the days, one of my profs at the University always had some cool quotes at hand. One of his favourites was “There is no such thing as a free lunch”. While I basically agree (at least what food is concerned), you often find free gems in the internet, like a series of JavaScript related books:
https://github.com/getify/You-Dont-Know-JS
They are available for free on github, however the author also sells them as e-book or even printed versions. I’m not sure if I would pay $17 for a 98 pages e-book which I can read for free, though… that sounds a bit too expensive in my opinion.