We all know the story of the shepherd boy who cried wolf. The boy decided to have some fun at the expense of the villagers. He shouted, "Help, help, the wolf is here." The villagers heard him and came to his rescue. But when they got there, they saw no wolf and the boy laughed at them. They went away. The next day, the boy played the same trick and the same thing happened.
Then one day, while the boy was taking care of his sheep he actually saw a wolf and shouted for help. The people in the village heard him but this time nobody came to his rescue. They thought it was another trick and didn't trust him anymore. He lost his sheep to the wolf.
The moral of the story is - When people tell lies, they lose credibility. Once they have lost credibility, even when they tell the truth, no one believes them.
Make yourself an honest man and then you may be sure there is one rascal less in the world. Thomas Carlyle