Regrets are the difference between what you did, and what you should have done. I think regret helps us focus on immediate areas of improvement. As long as regret lasts, it contributes to our thought process and our decisions. I think regrets motivate us to become a better version of ourselves, because they remind us that a better outcome could have been possible had we done the right thing. If you're not thinking about what you wish you did differently, how you could have prevented having this regret in the first place, then you're not regretting.
So... If you don't regret wasting your time, how can you become efficient?
If you don't regret causing someone to break down, who says you won't do it again?
I'm not talking about momentary regret where you just kind of feel bad/guilty but then forget about it by checking facebook. I mean lasting regret. The kind that makes you think "DAMN, why did I do that? Why didn't I do X instead? I so could have avoided Y & Z".
I think we need stop trying to always feel good about ourselves and occasionally let ourselves become vulnerable enough to admit our faults, to appreciate the pain we cause, and to truly remedy the situation if it isn't too late. Apologies are nice, but how about avoiding actions/words that would require apologies in the first place? Doesn't that sound like a good idea? But how can you ever achieve that if you don't truly take time to appreciate the consequences of your wrongdoings? THIS IS WHY YOU NEED TO REGRET.