Let’s think about the heuristic thus: suppose you were only rational, that is, you had no fear of death per se.
As you contemplate your life in the future, you expect both good and bad things. If you accept the coinflip and you “lose,” then your life comes to an end. You are deprived of the good things but relieved of the bad things. If you weigh up all those things and and find that somehow they exactly outweigh each other, then the coinflip is a wash. You get nothing if you “lose,” because your future will have nothing in it. But you also get nothing if you”win,” because then every good thing in the future that you will have is canceled out by some bad thing.
If you are a lucky person who expects more good things than bad in the future, then it’s just irrational to accept the wager, because your future contains good things of which you will be deprived that are not canceled out or outweighed by other bad things.
If you are not so lucky, though, then it is rational to accept the wager, because then you will be relieved of bad things while not being deprived of that many good things.