Koan - Buddhist

Two monks were arguing about the temple flag waving in the wind.
One said, "The flag moves."
The other said, "The wind moves."
They argued back and forth but could not agree.
Hui-neng, the sixth patriarch, said: "Gentlemen! It is not the flag that moves. It is not the wind that moves. It is your mind that moves."
The two monks were struck with awe.