"the whole world uses git" is a weak appeal to the masses (Argumentum ad populum), i.e. the popularity of git is no measure for its qualities, and we should collectively strive for better (just looking around should make it painfully obvious that there are many good things that git is lacking).

We previously saw that git is in fact two very distinct things: a repo format and a user interface; and we saw that git is too critical a mass to be dislodged as a repository format. The next best thing we can do is then to address its disastrous UX, and this is precisely what jj is about. And it tackles that without even incurring "contagious" changes in established organizations: neither you or I have to know/care whether others are using git-cli/vscode gui/jj/whatever.

This is progress, because teaching git to this day is in equal parts teaching "DVCS theory", git "the useful parts", git "the very many pointy bits not to get too close to", and git "I messed it up, please help me rescue my files". At least jj offers to simplify the learning while improving on the experience greatly, by offering a very cohesive, straightforward, discoverable safe and mostly trouble-free implementation whose tenets that can be intuited from the theory.

Knowing what RAM is and being an expert in it are different things though.

"git is the underlying protocol that jj is compatible with, and sites like GitHub speak git's protocol", there now you know what git is.