Once there was a boy who got angry every time something small happened. So, his father told him, that may be if you can mark when you were angry, it will be different. So, the father told his son to put a nail in a wooden board every time he got angry. The boy followed it for quite some time. Initially, there were few nails in a day. Then the boy noticed himself getting angry and was able to stop before he got angry, so the frequency of nails got reduced. Then there came a time, when there will be may be one nail a week. Then may be one nail a month. And then there was a month, where he did not have to put any nail in the board.
At this point, his father told the boy, that now, it will be reverse process. Every day, when he is not angry, he will need to remove one nail. The process went on for few years, but the boy was proud that at one day, there was not a single nail on the board. So, he told his father that I want to see the board. Now, it does not have any nail on it.
Father and son went to the board together. Father told his son that I am very happy about this. But do you notice anything on the board? The son said that yes, there are these nail marks everywhere. And so, the father said, that even if you can mend the effect of anger later on by some soothing words, there will be some marks always on the other person of that anger.