If time goes back and you have the choice either to:
- do something you did not do then.
or,
- not to do something you did in the past but you deeply regret it now and wish you have never done it.
What is such a thing? To make it clearer, this thing might be a decision you have taken or you did not take on time, a realtionship you broke, a job offer you accepted/rejected,...etc.