The great thing is that after reading and understanding these, one's mental model matches the reality of the Git program, so one can both try bolder things, and get unstuck from any mess.
Not to outright beginners, but anyone past that point should read this. It is a great job of clearly presenting an accurate mental model that helps you use git. If you are already a git expert this is just a good thing to learn from in general and with how to explain and teach git usage in particular.
The only documentation I know of that can turn people from cargo cult git users to people who just do the version control things they need done with the parts of git they need. That is damn useful.
* HTML version: https://jwiegley.github.io/git-from-the-bottom-up/
* PDF version: http://ftp.newartisans.com/pub/git.from.bottom.up.pdf (via http://newartisans.com/2008/04/git-from-the-bottom-up/)
The great thing is that after reading and understanding these, one's mental model matches the reality of the Git program, so one can both try bolder things, and get unstuck from any mess.