An angry boy

There was once a very angry boy. He gets angry over little things. One day, his father told to hammer a nail into the wall each time he gets angry. The angry boy did exactly what his father asked him to. He had to hammer the nail almost everyday. He feels that its very difficult to hammer the nail and its very energy consuming. Thus, he told his that about it and decided to change and not to be angry so easily. His father then told him to pull out each nail for everyday that he is not angry. He did as told. One fine day, he told his father that all the nails have been pulled out and said that he has learned not to be angry. His father looked at him as said, "Now that you have learned but the scars you left behind when you were angry can never be erased" as he pointed the holes on the wall.