In the Chinese classic《Chuangtze》(zhuāng zǐ 庄子),there is a legend like this:
Once upon a time, a gigantic fish named Kun (kūn 鲲) lived in the northern sea. No one knew how large it actually was. This fish could change itself into the enormous bird called Peng (péng 鹏), measuring thousands of kilometers in length. When the bird was spreading its wings, it looked like huge clouds in the sky. It could, in one stretch, fly from the northern sea to the southern sea on the other side of the globe and soaring up to 90000 li ( lǐ 里,1 li =45000 kilometers) in the heaven.

The bird can surely fly over a long distance without stop. Now people use this idiom to with others have a long career or a bright future.

很久很久以前，北海里住着一条巨大的鱼，名字叫鲲。没有人知道它到底有多大。这条鱼能够变成鹏，一种庞大的鸟，有几百万米长。鹏鸟展开翅膀就像天空里的一大片云。它能一口气从北海飞到地球另一边的南海。当它展翅高飞的时候，它可以冲上90000里的高空。

毫无疑问，这种鸟一次能飞过很长的距离。人们用鹏程万里这个成语来祝愿别人事业顺利，前途十分光明。

鹏程万里 (péng chéng wàn lǐ)
【翻译】A Roc's flight of ten thousand li-A bright future.
【释义】相传鹏鸟能飞万里路程。比喻前程远大。
【例句】中国的父母们都希望他们的孩子能够努力学习，将来才能鹏程万里。
【近义词】前程万里、前程似锦
【反义词】走投无路、日暮途穷