I often think about the Many Worlds Interpretation (MWI). Where for every outcome plays out in a different reality. You make a decision to go left instead of right, in this reality you went left, while a new reality split off and that other version of you went right. This is an over simplification of the implication, but it leads down some very interesting paths when you think about every choice you made in life.

I honestly don't really believe in regret. I feel that every choice made was what brought me to this exact point in my life. In general I am happy with my life, and therefore I am happy with my choices. That said MWI allows you to play through the scenarios, exploring what you think may have happened. It allows you to dream about alternate realities and consider what you'd be missing from your life. Since you can't know what you would have in these scenarios there is no point to dwelling on them, but you can with more certainty know what you wouldn't have for any major choice you've made in your life.

Where it gets even more interesting, is playing out scenarios of the choices made by those around you. How different would your life have been, from actions others took that you had no choice in but were still swept up in the wave of consequences?