Say you just deleted a branch or did a
git reset --hard <earlier commit> and in the process lost a commit which you intended to keep.
Well, the good news is that unless you have run
git gc to run a pass of garbage collection over your repo and get rid of objects which aren't linked to anymore, the objects for your lost commits should still be in the repo.
If you remember the SHA-1 IDs then you can simply use
git cherry-pick to apply them to the current branch. However, if you don't have these commit IDs anymore, there is still a way to get to them.
This command will display all commits from the most recent to the oldest one:
git log -g