I used Mercurial a lot before trying Git for the first time, the projects then switched to Git.
With Mercurial I felt right at home with the command line. Everything was simple and made sense, and I seldom had to consult the documentation after a short time learning it. I never felt the need for a GUI, or that it would improve things.
With Git it was the complete opposite. Nothing made sense at the command line. I had to do web searches for just about everything I did, either to figure out what arcane set of switches to use or to make sure I didn't fuck things up. After a short while I gave up and found a GUI, which made Git much, much better to use.
Perhaps things have improved somewhat, I hear they've cleaned up the command line options a bit. But looking at the manual[1] its clearly still far from Mercurial-level of usability[2].
[1]: https://git-scm.com/docs/git-reset#Documentation/git-reset.t...
[2]: https://book.mercurial-scm.org/read/undo.html#rolling-back-a...