I know this is a hard sell, but dying one day is a good thing: it drives urgency to accomplish a lot in your life; you get meaning through having children and raising them vs. living just for yourself; and (for the religious) if there were something outside of this universe, it would let you go back.
http://yourmeaninginlife.com/blog/the-science-and-meaning-behind-limited-lifespans
The problem with any behavior is whether someone unwillingly is harmed or pays the cost of another person’s behavior—not who benefits. Therefore, both selfishness and altruism can be bad if it someone else ends up being harmed or paying for it.
https://yourmeaninginlife.com/blog/non-consensual-harm-or-expense-vs-the-greater-good
You don't have to save the world; your life and world get better one day at a time with every constructive act you take.
https://yourmeaninginlife.com/blog/you-dont-have-to-save-the-world
You can always find a reason to complain, and you can always find a reason to be grateful. The former will lead to a miserable life; the latter will lead to a more pleasant life.
https://yourmeaninginlife.com/blog/it-will-always-be-something