I really like that poem "Ozymandias", by Percy Bysshe Shelley. The point of it is: no matter what kind of outsized impact you have on the world when you're alive, eventually no trace of you will remain, and everything you ever were and everything you've ever done will be forgotten.

It's a heavy, depressing message, but I find it to be oddly freeing. If nothing you do will matter in the very long run, then you're free to do whatever you want. Maybe you decide that you don't care about the people 25,000 years from now and focus instead on the people in your life right now. Maybe you make it your goal to make their lives better.

You could succumb to depression and fall into a pit of despair and heavy drug use... but if nothing matters, why not spend your time making other people's lives better instead? It feels good to make other people feel good.