One day the Buddha was waiting by the river bank for a boat to ferry him across the river.
An ascetic passed by and proudly showed off his miraculous power, crossing the river back and forth by treading over the water.
The Buddha smiled and asked him, "How long did you train to attain such power?"
"It took me thirty years!", said the ascetic.
The Buddha replied, "Thirty years? Well, I can cross the river using the boat for only one penny!"