I believe it was Mark Twain that once said:
"Twenty Years From Now You Will Be More Disappointed By The Things You Didn’t Do Than By The Ones You Did Do"
And he was certainly not the first nor the last person to make such bold statements on regrets, and given that we are all just human I doubt that there is anyone who has not encountered some form of regret throughout their life journey despite the fact that some might learn to acknowledge 'regret' as a crucial life lesson in stead of an anchor to their past.
Regardless of how you choose to view, remember or experience regret in the sense of: Things you could have done but did not; Things you should have done yet didn't; or even the things that you could have / should have done differently - it still remains an undeniable aspect of life encouraged by free will and as such the choices that we make.
What would your ultimate regret be?
For no other reason than creating the ultimate illusion where introspection becomes a necessity: Lets say that you knew that today would be your very last day on this earth, what do you thing your greatest regret would be, and in the respect of acknowledging it; Would you do it differently if you were granted the opportunity or do you believe that the series of preceding events (even if it might not be in your favor) were exactly as they should be?
"Yes, there are two paths you can go by, but in the long run,
there's still time to change the road you're on" ~ Led Zeppelin
The way I see it is that every single day might very well be our very last on this earth, and if you maintain a hindrance of regret, it splits our focus between the perfect beauty of the present and all that may come our every action here and now; And the past, that holds our unchangeable actions captive within its boundaries.
This does not mean that we do not have the means to change the things we regret, it merely mean that we have the opportunity to retrieve wisdom from actions that we can no longer change and ensure that we make better decisions in every action that follows, and in such actions radiate an inspiration that all others that are yet to encounter a pivotal point balanced on the scale between regret and jubilation, can nourish their own choices from.