Listen to him, full of ears, if you will be satisfied; What do you mean by asking for it and swinging around like the wind to catch the scenery?

Listening to them, my ears are full of beautiful scenes, as if I could see the gods soon; However, you are looking for it, but it is illusory, as if to catch a shadow. ...

There are also sources in Biography of Flowers on the Sea and Seeing the Present Situation of Monsters in Twenty Years, but Hanshu is its original source.

It means: good things can only wait, not be forced. Love is hard to find, so cherish it once you have the chance.

References:

A Dictionary of Chinese Idioms and a Dictionary of Modern Chinese Idioms