The Epic of Gilgamesh is considered the oldest surviving work of fiction, based around a real king and dating to around 2100 BCE.
When accounts were found in 1872 it caused a genuine crisis of faith in Victorian England with the implication that the flood story predates Genesis, suggesting the bible borrowed from an older source.
Gilgamesh was part god, impossibly strong and a tyrant. The oldest surviving story in the world is about a man having a breakdown about mortality.
Gilgamesh and Enkidu become friends and fight together including a bull of heaven which offended the gods enough to demand a death in return.
The gods punish them for this act by killing Enkidu which takes twelve days.
Gilgamesh watches.
Gilgamesh can't handle it, he leaves his life behind to travel to the end of the world to find Utnapishtim, the only man to ever be granted immortality. Utnapishtim tells Gilgamesh that this was a one-off, that he survived a great flood and when the gods found him, they made him immortal as compensation.
As a last hope, Gilgamesh retrieves a plant from the bottom of the seas that restores youth but a snake eats it while he's asleep and so Gilgamesh goes home and dies.
It's as simple as that; Gilgamesh wanted to live for ever and he didn't, that's it. Seeing his best friend die slowly broke something in him; the primal panic of realising death is coming for him too.
Every story that comes after is essentially a footnote to Gilgamesh and no one has come up with a better response than refusing to accept it, failing to prevent it and going home anyway.