'Tis easy to find a staff to beat a dog.

The proverb suggests that someone determined to punish another will have little trouble finding a reason, whether or not that reason is fair.

Its point is less about the alleged fault than about the punisher’s intent: a ready-made justification may conceal a decision already made.

Use it to question a complaint or accusation when the person making it seems eager to penalize someone and quick to seize on any available fault.