You just want the time clock to go in reverse so that you can go to a moment/phase in past and undo the things which you did wrong at that time.
Since most of the times you cannot turn clock backwards, you just keep on regretting about things. Some people say regretting about past things/actions is not a good thing - one should move on and blah blah... But I feel regretting is a way of reminding to yourself that you did something wrong. To have that guilt feeling burning in you keeps you on toes to not commit the same mistake again.
This is also necessary since some mistakes last for a lifetime.
Only if I could have...