Pride is an emotion that intelligent creatures can easily generate. Whenever they achieve a considerable accomplishment in a particular aspect, this emotion tends to develop within them.
For instance, back then, when Muria resided on Taiji Island, there was no other worthy adversary in his sight, not even the most powerful Storm Giant was more than a match for him. Even in such a situation, and despite knowing of other beings similar to him around the world, he was still inflated with arrogance.
It wasn't until later, when he traveled to the Titan Tribe Lands and fought the Titan tribesmen, was his arrogance ground away.
Quite obviously, Dragon Mother Atris had a similar background when she was young. No same-aged dragons she came across were a match for her, thanks to her potent ancestral dragon bloodline. This led to the birth and amplification of her arrogant heart.
