The dog is a useful domestic animal. But it is always possible to brand it as a mad dog and kill it. If somebody says that the dog has got rabies, others will also think that it is true. The poor creature cannot speak out for itself or prove its sanity. This is true in the case of human beings also. A person may be good and innocent. But other people jealous of him can brand him as a bad man. Such talk will soon spoil his image and others also might believe those false things about him. The poor man may not even know that his reputation is being tarnished. As he is innocent and good, he will not think that others will speak such things about him. Once such an impression is created it is not easy to erase it. People have a tendency to think that once bad is always bad. Even though in reality the person may be good and innocent, he gets a bad image. The proverb means that it is always easy to brand somebody as bad crucify him although he may be innocent.