English: Rabbi Shimon said: Such is the punishment of a liar — that even when he speaks the truth, no one listens to him. So we find with the sons of Yaakov: it is said, “He recognized it and said, ‘It is my son’s tunic’” — therefore later, even though they spoke the truth, he did not believe them, as it is said, “and his heart went numb, for he did not believe them.”
On the daf / in context: Avot de-Rabbi Natan links Yaakov’s initial disbelief to the earlier false report the brothers had given about Yosef’s death.
Type of Learning
Derash on the verse (Avot de-Rabbi Natan) — not a formal named middah of the 13.
What Is Learned
One who has previously lied loses credibility even when he later speaks the truth; Yaakov’s initial disbelief is the consequence of the brothers’ earlier deception.