Git: Undo a Git Mistake

git reflog is a record of your actions in Git. With this command, you can undo almost any Git mistake.

$ git reflog

4bd0090 HEAD@{0}: <bad place>
46bd839 HEAD@{1}: <bad place>
967e214 HEAD@{2}: <last good place>
46bd839 HEAD@{3}: <good place>
967e214 HEAD@{4}: <good place>

$ git reset --hard HEAD@{2}

Via jwworth/til.