The unpredictable changeability of worldly affairs; literally describes white clouds transforming into the shape of a gray dog.

fleeting and unpredictable changes in human affairs, literally meaning gray dogs and white clouds

Describes the rapid and unpredictable changes in human affairs or the world, like clouds shifting from the shape of a white shirt into a gray dog; originally from Du Fu's poem "Ke Tan" ([[可叹|可嘆|ke3 tan4]])