The gemara in Sota tells us the because Yehudah pledged to give up even his olam haba should he fail to return with Binyamin, his bones rolled in his coffin as Bnei Yisrael travelled through the midbar and he was not admitted to gan eden. Moshe davened for Yehudah, asking that in the merit of his causing Reuvain to admit to misdeed and do tshuvah, Yehudah should be admitted to gan eden. Reuvain had sinned by moving his fathers bed into Bilha's tent after Rachel's death, and only admitted his wrongdoing when he heard Yehudah, at the expense of great embarassment, admit to being the the father of Tamar's children.
R' Leib Chasman, in his eulogy for the Alter of Slabodka, asks on this Chazal, why did Yehudah gain entry into Olam haBa only based on his causing Reuvain to admit guilt - why would he not gain admission based on the merit of his own admission of guilt? R' Leib Chasam explains that the true measure of a person's greatness is their ability to influence others. Yehudah's influence on Reuvain was a far greater measure of his true character than his own personal admission of guilt.