With hundreds and hundreds of comics containing tales of supervillains trying and failing to kill heroes, it's all too easy for comic readers to become conditioned and expect their heroes to survive. Much like Thanos, it's inevitable that after reading countless issues of your favourite do-gooder escaping death's clutches, it starts to feel like their plot armour is so thick that there's no way they could actually be killed.
This is why it's absolutely crucial that there are occasions in which a hero's nemesis does kill them, as it not only fixes this disillusionment, but also reinvigorates the big feuds that DC and Marvel live on.
While even death has a habit of not lasting long in comic book universes, seeing seemingly invincible characters like Batman and Thor slip up and be murdered always feels like something special, even if you know it isn't a permanent affair.
It's a move that can admittedly easily be overused - as is best shown with heroes like Jean Grey, who are constantly reincarnated - but, given an intense enough rivalry and a dramatic enough death, it can also be exactly what a plot needs to have that little extra punch when you read it.