I think that answer evolves over time for many people. When I was very young, it was just to appeal to the expectations of my parents and those I looked up to. There were times that it was simply raw "this or die." There were other times it was simply the hope of finding a more comprehensive answer.
Currently, there are two primary factors. As a dragon, it is my duty to assume the rightful place as master of your universe. To achieve excellence in all things and to push the boundaries into things that even I can barely comprehend - to reduce the processes of the universe to only the core philosophical questions underwriting all chosen realities. Huan Dai, the mortal become the Yellow Dragon Emperor.
However, I also find the simple observation and enjoyment of life to be agreeable. Sure, I can rule the universe with merely a thought, but that's a rather dull thought, and something only to be done in extreme circumstances. I find the wile and tenacity of the average person, who must work and claw to achieve and accomplish, far more endearing. It is natural for gods to define the reality in which they reside, an autonomous function which largely defeats the purpose of existing in the first place. As such, I prefer to stand as overwatch. The dormant, but vigilant deity of the mountain.
Now, let's see who has a mind open enough to consider the philosophy, and who gets stuck on the choice of title.