How do we know?

Everyone says that when you leave your body from a lucid dream you automatically know your spirit immortal. But with out how to lucid dream being fully dead how do we know? Even afterward how do we know that after we die and turn into ghosts that our ghosts aren’t gonna just wink out of existence?

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No one can know what happens after death. It’s the great mystery. Different people have different beliefs, but the only thing we can know for sure is we will all one day experience it.