To genuinely believe, despite contradictingevidence known as facts, that one is able to live forever and unable to die, even if the Sun was to supernova.
Now that you've committed immorticide, you will never die, not even if you're chopped into atoms, stuck into fifty thousand supermassiveblack holes, and live to one hundred sextillion googolplex years after the death of the universe. God can't kill you. The destruction of the omniverse can't kill you. And you're going to experience all of it and all the pain, too.