Constant dropping wears the stone.

滴水穿石。 

Joke of Today

    A man calls the Animal Control in his town, because there is a crazed gorilla on his roof, and he can't figure out how to get it down safely. Soon, a van pulls up, and an old man gets out, carrying a small dog, a baseball bat, and a gun. He hands the man the gun.

    "Okay, here's what we do. I'm going to go up onto your roof, and threaten the gorilla with this baseball bat until he falls down. When he falls down, this little dog will bite him in the balls until he's incapacitated."

    "Great," says the man. "But what's the gun for?"

    "In case I fall down instead of the gorilla -- shoot the dog."