The answer is actually quite simple: If your mindset is that there is / there should be something to regret and that this is significant, you'll find it or even invent it. Those who regret and beat themselves up are those who look into the past and/or worry about the future way too much to the point of abandoning the present moment, the now, which is in fact all they have, so they should simply witness it. The past is in the memory, the future is in the imagination. I call this "getting too involved with the game". However, if your mindset is that you are just passing by, playing and gaining experience, and that after your physical body (which is not the real you!) dissolves you'll eventually come to another experience, you'll hardly find anything to regret. You'll have the eternity and this particular life is just a tiny fragment of it - one of your roles. If this is true, why worry? On the other hand, if this is false, then there is no point to worry, because when you are dead, nothing matters - when there is no you, there is no world. By the way, your body is constantly dying and coming to life again. Your cells die and new ones come. Where is the you from 10 years ago? It's dead. It's all about transition. And all these elaborations vanish with the state of ultimate existence - when one realizes that one is pure awareness beyond the body-consiousness. What and where is "I"? It's not our body and we cannot point it - we even say "my head, my heart, my hand, my thoughts", which are not "I".
Funny, it's only now that modern science barely scratches the surface of what spiritual teachers and philosophers know for centuries.