One of the worst things that can happen to you in your life is having regrets. To have regrets is horrible, unsustainable and above all immutable.
When we regret something, in most cases we can not act on it anymore.
Because true regret concerns events that belong to the past.
The past can not be changed and we Must accept that!

If you ever feel regret about a recent event and can still act on it, do it as long as there is still time. Repeat the project you abandoned, break the silence by talking to the person with whom you are angry, take your courage with both hands and go see that person whom you have been watching for so long.

I think you got the idea: Act today to avoid having regrets tomorrow.

An important note that I want to add :
If you have real regrets on which you can no longer act, pay no attention.
I know that what I just told you is very difficult to apply and that this advice deserves more than just a sentence, it deserves ACTIONS.

Just remember that regrets must be identified, understood and internalized.
You must not forget them: they are part of your life course. You must accept them so that they do not periodically return to the center of your concerns.
Always remember that you did what you thought was right. You did what you had to do to make it to where you are today.

Don’t look back in sorrow. Simply let it be and look forward to your infinite future.