A monk decided to meditate alone, far from his monastery. He took his boat to the center of the lake, tied it there, closed his eyes, and began to meditate. After a few hours of silence, he felt the sudden thump of another boat colliding with his own. With his eyes still closed he felt his anger rise. He was ready to yell at the one who had so carelessly disturbed his meditation. But when he opened his eyes, he was surprised to discover that it was an empty boat that had hit his own. It had probably been untied and was floating towards the center of the lake.
At that moment, the monk had a great revelation. He realized that anger was within him; he only needed the blow of an external object to get it out of him. From then on, whenever he encountered someone who irritated him, he reminded himself that the other person was nothing more than an empty boat: anger was inside him.