I thought of a scenario. It's all made-up, so no "but this couldn't happen", so in this scenario this is what happens.
Let's say tomorrow a way to make people immortal is achieved. Immortality engines are built and everyone can become immortal.
However, there's a catch. The Immortality Engine fixes all your diseases and makes you young again, something like 25 years old with no diseases of any kind. However, to do this, the Immortality Engine needs the original you to make the undying undiseased you. All your knowledge is preserved, all your emotions, memories, etc, all preserved, just that your body is made 25, healthy and immortal. In case by some accident you'd die, the Immortality Engine would make a new you. To counter for this, we colonize other planets, so space and resources are not an issue.
However... to make the "perfect" you, the Immortality Engine destroys the original you. All your knowledge, memories and emotions are transmitted, you can still learn new stuff, experience new stuff, etc. But the truly original you is gone. And here's the catch, to live forever, you'd only do so by the memories of your exact clone (in terms of memory, experiences and emotions, body wise it might be a bit different unless you're already 25 and healthy).
You have 1 month to chose:
-you can enter the Immortality Engine, become immortal and forever healthy but through your clone, while the original is destroyed. However, if you belive your conscience or soul or whatever you belive in is transferred, then you have nothing to worry about... but you can't say for certain since other clones of people you knew say they're the same, but are they, or is it just because the Engine copied them perfectly?
-you can decline the offer, however, because the people who accepted the offer never want to suffer again after losing a loved one, you'll be exiled to a planet similar to Earth with other people who declined where you can live your life as you do today and die, to forever be dead.
What would you chose?