I focus on this part. What's done is done. Work on what can be controlled or changed, not what can't. There's a lot of things I would do differently if I could go back in time, but those aren't things I can change. There are lots of things I am in control of now, and every action I take today matters.
A strategy that works for me is to have every moment be a starting point. If your goal is to eat healthy, for example, the fact that you ate an entire cake for lunch does not influence whether you eat healthy or not for dinner. Previous bad decisions (or things you regret) do not give you a pass to continue them, nor does making good decisions give you a freebie to make a bad decision. Maybe cleaning the house would have been better had you done it in the morning. If you instead watched a Law and Order SUV marathon until late afternoon, that doesn't mean you can't still clean the house. When you woke up that morning, the best time to clean was after breakfast. After your TV marathon, the best time to clean changed.
Regrettable things don't have to be chain reactions is what I'm getting at. You can't go back and do or not do things you regret - but they don't have to have any bearing on future action or decisions you make. Not doing things in the past doesn't stop you from doing them in the future. Breaking one thing doesn't stop you from building something else. Keeping those things in mind is what helps me with things I regret, whether they are big or small regrets.
