For me, personally, I don't fear death. I know people that are religious and they are convinced that if they don't act a certain way they will be tortured for all eternity. As an atheist, I try my hardest to help them not fear death because I used to fear hell myself. I tell them how often do you worry about the other versions of hell in other religions? It took me a good three months to finally let go of my religious childhood indoctrination. And it is possible to do so.
But hell is not the only reason. Some people don't like the idea of never existing again. For those people, I try to explain to them how they felt not existing for 13.8 billion years before their birth? Not existing isn't an experience, you won't even know you're dead.
Lastly, there is the fear of never seeing your friends or family again. And I can relate to this one a lot. I don't want this to be true, but if I'm thinking logically it makes perfect sense. I try to explain to them that you won't be sad because you won't exist. And hey, for some reason if there's an afterlife anyway then it's a bonus. Just don't live your life in fear and cherish the time you do have.
I hope this helps people that fear death. If I can get over it so can you.
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Fear of the unknown.