The Yetzer HaRa ,evil inclination, is like a prankster running through a crowd showing his tightly-closed hand. No one knows what he is holding. He goes up to each one and asks, “What do you suppose I have in my hand?”
Each one imagines that the closed hand contains just what he desires most. They all hurry and run after the prankster. Then, when he has tricked them all into following him, he opens his hand. It is completely empty.
The same is true of the evil inclination. He fools the world, tricking it into following him. All men think that his hand contains what they desire. In the end, he opens his hand. There is nothing in it and no desire is ever fulfilled.
Worldly pleasures are like sunbeams in a dark room. They may actually seem solid, but he who tries to grasp a sunbeam finds nothing in his hand. The same is true of all worldly desires.
Rebbe Nachman, Sichot HaRan #6