Oh Shit, Git?

I believe I have a good mental model of what git does, but I never remember commands' arguments to use when they are moderately complex. I mean that the commands are not discoverable or easy to memorize.

I don't know if that's because the text UI is bad, or because it's simply difficult to explain with text what to do to manipulate a tree.

Both.

Manipulating complex trees via text is not easy, but the text UI is objectively bad:

https://stevelosh.com/blog/2013/04/git-koans/