If it happens past your lifetime, it doesn’t matter. These sayings are meant to apply to you, not history.

I look back to the serenity prayer, which is really just a bit of Buddhism: “Lord, let me accept the things I cannot change, change the things I can, and have the wisdom to know the difference.”

The Buddhist path is "why is there suffering in the world? Because of attachment. You want things to stay the same. Things change. You want your parents to live forever. You don’t want to be sick. You wish your job didn’t suck. Why can’t I just win the lottery and have my problems go away? You want to cling to the good times and not have the bad. You can let go of the bad, and the resultant suffering because of it will fade. Letting go is incredibly hard, because our biological bodies are hard wired on routines. But if you can overcome that, and accept that whatever happened, happened, you can move forward. You can’t change the past. And whether you like it or not, time and the world moves forward. You can move forward with it, or let something hold you back.

And just to clarify, I’m an atheist, so my understanding of both the Serenity Prayer and Buddhism are seen through the lense of someone that doesn’t believe in an afterlife or religion in general (strict Buddhism is not a religion). I encourage you to find your own conclusions.