when you done something wrong and you want to discard changes
git add ccc.txt
after track file you can saw your branch status like below
On branch master Your branch is up-to-date with 'origin/master'. Changes to be committed: (use "git reset HEAD <file>..." to unstage) modified: ccc.txt
maybe after meeting with your boss,you have to do rallback your code
git reset HEAD ccc.txt
git checkout -- ccc.txt
now you did rallback your code already.