The principle is that a person's plight is hopeless once his reputation has been blackened. Similar to he that has an ill name is half hanged.
s.v. Perro, We say, Give a Dog an ill name and his work is done.
[1706 J. Stevens Spanish & English Dict.]
Give a Dog an ill Name, and he'll soon be hanged. Spoken of those who raise an ill Name on a Man on purpose to prevent his Advancement.
[1721 J. Kelly Scottish Proverbs 124]
It is an old saying, ‘give a dog a bad name and hang him’.
[1803 Norfolk (Virginia) Herald 14 Apr. 3]
The Liberal impulse is almost always to give a dog a bad name and hang him: that is, to denounce the menaced proprietors as enemies of mankind, and ruin them in a transport of virtuous indignation.
[1928 G. B. Shaw Intelligent Woman's Guide to Socialism lvii.]
Give a dog a bad name seems to have become a workaday motto for the wine trade. And the sillier the name on the bottle, the less chance there is of anything drinkable inside.
[2002 Times: Weekend 20 July 4]
Related to: reputation; slander
Bibliography of major proverb collections and works cited from modern editions is available here.
