Death.
Every living being in this world was destined to die. Whether they die young, in an incident, or perhaps in old age, eventually, their corpses will be covered by dirt. All the meaning of their existence is nothing but a tombstone, and the meaning of their existence was a small phrase of their epitaph.
However, even if this was a given fact that humans already knew, most of them were still afraid of death.
Why? For what reason?
It was simple. Because they have dreams. Humans wanted to define and have their exitance a meaning. They fear living aimlessly without making any difference. That was why most people dreamed of becoming a hero, wanting to have their names written in books and be defined as legends.
Who wouldn't want fame? Wealth? And even respect?
None.
In the deepest darkest part of a human's heart, desires exist even though they thought nothing; Not even the slightest emotion could exist anymore.