Up to this point in the epic, Gilgamesh is feeling invincible.       However, why is he making a very big mistake feeling this way?

In the Epic of Gilgamesh, Gilgamesh initially feels invincible due to his demi-god status and his great strength and accomplishments. However, this is a big mistake for several reasons:

1. Overconfidence: Gilgamesh's feeling of invincibility leads him to take unnecessary risks and make poor decisions. For example, he challenges the gods by killing the Bull of Heaven and Humbaba, which leads to the death of his best friend, Enkidu.

2. Ignorance of mortality: Despite his demi-god status, Gilgamesh is still part human, which means he is mortal. His feeling of invincibility blinds him to this fact. It's only after Enkidu's death that he truly understands his own mortality.

3. Neglect of responsibilities: As the king of Uruk, Gilgamesh has responsibilities towards his people. His feeling of invincibility leads him to neglect these duties, causing suffering and discontent among his subjects.

4. Disrespect to the gods: In Mesopotamian culture, the gods were to be respected and feared. By feeling invincible, Gilgamesh shows disrespect to the gods, which ultimately leads to his downfall.

In conclusion, Gilgamesh's feeling of invincibility is a big mistake because it leads to overconfidence, ignorance of his own mortality, neglect of his kingly duties, and disrespect to the gods.