John sat underneath a cherry blossom tree one day with his Zen Master listening to a cuckoo bird that was sitting on a branch.
The Zen Master looked up from his mediation and asked John, "What is the purpose of the cuckoo's existence?"
Not able to come up with a suitable answer, John replied, "I do not know."
The Zen Master picked up a nearby stone and asked, "What is the purpose of this pebble's existence?"
Still not able to answer, John replied, "I do not know."
Finally the Zen Master asked "What is the purpose of your existence?"
John thought that it was a trick question so he again replied, "I do not know."
John then watched as the Master threw the pebble at the cuckoo, who quickly flew away.
And thus John was enlightened.