When a colleague generated a dia graph for each git object that got created when he made a few commits. Understanding the underlying data model was a real aha moment. 13 years later and I'm still grateful for his "mini git course".
That time I accidentally wiped an entire open source project on github and had to learn real quick how to undo a destructive commit.
Somehow after an entire night of google-fu, reading the git book three times, and tutorial videos, I got the right series of commands to fix it and nobody ever figured out what I did.
All I wanted to do was fix a typo in an imported module...
You never reach a phase when you can confidently say that you understand git. But it's certainly possible to go from "When something goes wrong, I just delete the repo and clone it again" to "Aha! Now I can deal with most of the issues".
Mine was when I realized that git commands come in two flavors. Those that deal with commits as snapshots (commit, checkout, switch, reset, etc) and those that deal with commits as changes/diffs/deltas (merge, rebase, cherrypick, revert, etc). (Note: This isn't about how git stores commits on disk). I believe that this is actually the main source of confusion for beginner and intermediate git users.
When I learned about the reflog. I became less afraid of my changes when I knew I could easily recover from my errors. This allowed me to experiment more with git and become more proficient in it.
Another aha moment was learning that an easy way to squash commits is just to do a git reset followed by git commit -am “whatever”
I initially just used it on personal projects just so I could rollback if I needed to. Afterwards I realized that you could branch after watching Fireship videos. I never got an aha moment, but the moment I really understood was after my first pull request to a project I liked at the time.
I discovered it, along with other DVCS when it came up, and looked into it and learned it. It was reasonable and intuitive enough for me. As far as I can remember anyway. (I don't have particular memories of that.)