It can be said that we become aware of our "self" when we start relating feelings and ideas together to form an opinion of our "self". This is how we define our "self". The problem is that our concept of our "self" is relative to the moment in which we perceive it.
I believe we all can recognize that a single event can forever change our self reflection, a car accident, the death of a loved one, having a child, etc. Major, life-changing, events can obviously have a profound impact on how we view the world. However I don't think we tend to give as much consideration to the impact of the minutiae of life. We seemingly tend to ignore how it reflects in our self image.
The philosopher David Hume in one of his more well know works, A Treatise on Human Nature, wrote
"It is plain, that in the course of our thinking, and in the constant revolution of our ideas, our imagination runs easily from one idea to any other that resembles it, and that this quality alone is to the fancy a sufficient bond and association. It is likewise evident that as the senses, in changing their objects, are necessitated to change them regularly, and take them as they lie contiguous to each other, the imagination must by long custom acquire the same method of thinking, and run along the parts of space and time in conceiving its objects."
This, to me, speaks to the very heart of my point. We don't have a constant self to reference. Our image of self changes based on our environment. If reflecting one's self while depressed, one is likely to see a less appealing picture. If reflecting while angry, one may see rage personified.
What I see as regretful today, while it may have also been regretful yesterday, may not always be regretful in my mind's eye. As time and life flows onward, my view of the world contorts and reshapes itself in an instant. Decisions that are major milestones in someone's life line may have been insignificant when they were made. For example, taking an alternate route to avoid traffic is rather insignificant, until having a major accident on that new route makes it a life-altering decision.
Just as minor decisions can play out with major consequences, the opposite can be true. For example a decision on which college to attend means nothing; if the student gets an employer that places no value on academic prestige.
I look at life as a journey from point A to point B. It is not that I think we are predestined. I don't believe that point B has been fully defined. Instead, I think the route is made up as we travel the path, but when we arrive at point B that is exactly where we are supposed to be, regardless of how we got there. A favorite song lyric comes to mind, it was in the song "Oh Me" by The Meat Puppets and made famous by Nirvana.
I don't have to think.
I only have to do it.
The results are always perfect.
But that's old news
Why live with wasteful regret? It just dilutes any thing that resembles positive self image, and wears like a heavy fur coat on a hot summer day. Wasting time with regret prevents joy of life in the present. We have all more-than-likely heard the expression "We'll look back on this in a few years and laugh..." What is this if not simply another way of saying that time will change your perspective in relation to this moment?