I try not to hold on to regrets if I can help it. It does not always work of course, but I generally reach the conclusion that a situation did not work out the way I wanted because it was meant to happen that way. There have been job interviews that did not materialize in employment, aborted travel plans to places I have yet to visit, and sometimes not making the kind of impression I want to make due to nervousness or other reasons. Instead of focusing on the past, even if it was only yesterday, I make sure that every day I try to make things better better for myself. It's not always easy, but I usually adhere to this way of thinking and it does help. Of course it can be difficult to do this when there are people around me who wallow in their regrets, and try to make me do the same.
I purposely try to keep away from people who are regret-ridden (of the non-criminal variety of course), but there are those in my family and associated with friends who I cannot always avoid. I do my best to tolerate their behavior, and stand up for myself when needed. Sitting through stories from people who regret their marriages, or how they are afraid to go back to school because of how bad they were in academics as children, or how much they hate their current or past jobs are normal unless they are repeated ad nauseum and those telling the stories have learned nothing from them. When I try to alleviate the mood by telling some to look forward to today and tomorrow, I am sometimes ignored, get a roll of the eyes, and occasionally I am heard.
We have to make the best with the time we are given; that goes for all of us.