I have been using Git a long, long time. I have worked on Git clients and libraries. At some places I've worked, I am the person folks go to when they need Git help.

And yet, only today I learned you can pass -m to commit twice (or more) and it will do the right thing of making each successive message a new paragraph (which is useful for the convention of a short summary as a single first line and following paragraphs as a more detailed message).