A reputation for unwavering truth makes lies more persuasive. [contrarian]
But the point is that his enemies did not know this. They thought that Yudhishthira could never be motivated to deviate from the path of truth. This is why the lie worked.
QUESTION: What does this suggest about strategic deception elsewhere—does credibility amplify the impact of rare deviations?
Diego Gambetta, Trust - Making and Breaking…, loc. 821