In the Diamond Sutra, the Buddha said: 

All things born of conditions are
Like dreams, illusions, bubbles and shadows
Like dew beads and also like lightning flashes.
Should contemplate them in this way.
Things arise from a confluence of conditions are considered as conditioned dharmas. They are merely conceptual and impermanent. By contemplating everything in this way, we can let go all worldly attachments and see the truth eventually.