We all fall down

The authors of the book stress that although Gilgamesh is two parts god and one part human, he is just as vulnerable to mortality as any other human being is. This clearly shows that the authors care about the universal equalizer of death, and that all who roam the earth, even heroes, are not immune to the fate we all share. After his search for Utnapishtim, the only mortal to be granted eternal life, Gilgamesh learns that he has limits as to what he can achieve, despite his unrelenting feeling of entitlement. By not being able to stay awake for a week as Utnapishtim challenges him, he is forced to recognize that his abilities do indeed have human parameters. Even though Gilgamesh possesses abilities far beyond any other mortal with unparalleled strength, wisdom, and aesthetics; he too suffers the fate of unavoidable decay.
The authors found this point prominent because in their era live wasn’t all sunshine and daisies. The Mesopotamians used the Gods as a source to answer all they found to be unknown, and assumed that all harm in their world was whiplash from the Gods which initially sprung from the actions of mortals. The Gods were the only all powerful beings, and any mortal could lose the favor of the Gods with their actions, just as Gilgamesh did when he turned down Ishtar which resulted in the death of his dear friend Enkidu. The authors wove the point of mortality and inescapable vulnerability to the Gods throughout the novel, and built all the details from this sole establishment to add a sense of security to their existence, even if this security was founded with death and the subjective actions of a higher power.