What is regret? Is it a feeling that is felt when we do something wrong, or when we don't do something true? Both of them or none of them?
Sometimes we turn back, and take a look at what we did, and sometimes what we didn't do. Then regret lays over us. It's like guilt, but actually it isn't. It isn't like remorse, too. Maybe the desire to impossible, the desire to missed stuff. What do you think about it?