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.