According to Zhuang Zi, one of the most influential Chinese philosophers and the main co-founders of Taoism, there was a gigantic fish named Kun in the northern ocean, whose size was too huge to be counted.
This fish could turn into a bird with the name of Roc, whose back was thousands of li (half of Kilometer) in width. When it spread its wings and flew, it seemed like clouds all round the sky.
When the bird was moving to the Southern Ocean its wings flapped the surface of water with more than a 3000-li high slash. Then it soared on the whirlwind up to 90,000 li in the sky. It seemed to bear the blue sky on its back, and there was nothing to obstruct or arrest its course. It could easily pursue its way to the South without rest.
The knowledge of that which is small does not reach to that which is great; the experience of a few years does not reach to that of many. The mushroom of a morning does not know what takes place between the beginning and end of a month; the short-lived cicada does not know what takes place between the spring and autumn. These are instances of a short term of life.
In the same way, what should the small sparrow know about the matter of the Roc?
Background and Writer Comment:
This idiom story is from "Enjoyment in Untroubled Ease (逍遥游)", an article of Zhuang Zi, in which he used this story to illustrate his theory, that is as mentioned above, "The knowledge of that which is small does not reach to that which is great".
Later generations use this idiom "The 10,000-Li Flying Range Of The Roc" to describes a bright future, or wish someone success in his or her endeavor.