This is all you've got, buddy. Nothing but death at the end, but that's OK. Immortality isn't about living forever, or about heaven, it's about some part of you surviving death and that part is the memory of you people carry around in their heads once you check out. It's brief and the memories quickly deteriorate, like the ring of a bell.

Even with that dismal description, you can be at peace with mortality and you don't have to use religion to fool yourself with some fantasy of Celestial Candyland. It's hard to confront mortality, and plenty sad, but it contrasts with living and that can be wonderful in spots for lucky people like us who have the good fortune to have so much that delivers pleasure, helps us avoid pain, and puts us in proximity to other people we can touch, love, help.

But good or bad, Hitler and Buddha both suffered the same consequences as your great, great grandfather... they died and are gone now, and powerless to affect you other than what you can glean from their lives that is worthwhile. You owe none of them anything. You owe no one anything. Your job, if you can pull it off, is to wake up tomorrow morning in one piece and repeat. If you WISH, you can accomplish something that helps you be happy and if you are KIND, you will do things that don't make other people unhappy or hurt them. If you are WISE, you'll look for ways to help and make the effort to do so. You'll GROW as long as you can. Morph into a better you. Show lesser folks (in age and wisdom) the way it CAN be done.

Note that if you were a lower life form, your options would be to avoid death and deliver it.... me, me, me! All the time. As a human, you have the ability to choose, reason, and act to change your circumstances. You can be all about the other, as christianity preaches (but usually doesn't practice.) It's how the species COULD evolve, with effort and self-sacrifice in the interests of your brothers and sisters on this planet. If you subtract out the nonsense of religion involving god and the afterlife, it means you can choose a life that is aimed at something other than you..... and that can range from being accomplished at something that is of value to the world, or helping your fellow man understand it better, or working for causes that benefit both our species and the ones that we depend on (and vice versa.)

Life really is what you make it. Unexpected bad stuff that happens is no more avoidable than intentionally created good stuff that you can cause to happen.

In the end, no one really cares if you are happy or not more than you do. Nature just wants you to execute the "live long enough to breed and do so, however you must" algorithm and if you look at your design, you'll see once you do that, Nature is done with you. You can add to/modify that job description, but that's entirely up to you.

What are you going to do with your brief time?