"You cannot undo what you have done."
Simple, obvious, yet with greater consideration than a surface analysis it becomes almost a life changing idea. The idea itself is a truth, that we are only masters of our present and cannot change our past no matter how much we re-consider it. Consideration needs to be placed therefore on the vast consequences of our actions in the present, for they lead to the future in which the present becomes the past. Therefore our present defines where our future leads, not like we can know the consequences of each action/inaction but we can have at the very least a general idea.
What that all means is, much more time (almost all of it in fact) should be devoted to thought about the present. The past is a tool for learning and the future a reality that must be considered but both of these should play a very small role in your thinking. The impact of doing/saying or not-doing/saying something can be very minor or major but there will always be an impact. There is always ripples that creep into every other facet of life. I have found, time and time again that my focus on my future, where I want to end up, has caused me considerable disappointment, distress, anxiety and anger in the present. Instead of being satisfied with the stage of my life I am in, I seek after things I think I want. It has been a constant theme to my thoughts that I think not about the present (the journey) but instead about the future (the destination).
I'm very tired of being disappointed with my present. I was asked a few questions before I left home by a few people about what I look forward to most and in all honesty I often answered "coming home". Bizarre and no longer true, it was because coming home to me was coming home to a job I love and another summer in the home that i'm madly in love with (ask anyone i've met on my trip, i cannot STOP gloating about NZ.)
Your actions in the present seriously impact what will be possible in the future. Careless words or actions cannot be unsaid or undone. You can mitigate their effects but only so-far. This is part of why I seek after God so often when I am afraid of the present. I spent a time living in fear of doing, and so I did nothing which changed what my future could hold. I feared being bad at anything, so I didnt try any of the things I wanted to. Now my present (the old future) lacks me being able to play the piano, having a developed voice, being as fit as I wanted to be, knowing another language. How seriously my life is different because of these choices.
I decided to accept regrets as part of my life because I don't want the fear of regretting doing something to stop me from doing it. It is better, in most cases, to regret doing something than not doing something so for me the idea is more "you cannot re-do something you never did". It just sounds neater the other way around.