There is no joy for the wise man like his joy over the correction of his character traits
A truly wise person rejoices if he has managed to correct a character trait that was previously flawed in him.
("And there is no pain for the wise man like his pain over his failure in a trait of disgrace, and there is no joy for the wise man like his joy over the correction of his character traits, as in the story of the pious man who lay in the corner of the ship and did not get upset at the one who cast refuse upon him, and rejoiced greatly when he felt within himself that he was not upset" - Chazon Ish / Emunah U'Bitachon, IV, 15)
Translation
Expression (Hebrew)
אֵין שְׂמֵחָה לֶחָכָם כְּשִׂמְחָתוֹ עַל תִּקּוּן מִדּוֹתָיו
Definition (Hebrew)
הָאָדָם הֶחָכָם שָׂמֵחַ אִם הִצְלִיחַ לְתַקֵּן תְּכוּנַת אֹפִי שֶׁהָיְתָה לְקוּיָה אֶצְלוֹ.
("וְאֵין כְּאֵב לֶחָכָם כִּכְאֵבוֹ עַל הֶכְשֵׁלוֹ בְּמִדָּה שֶׁל גְּנוּת, וְאֵין שִׂמְחָה לֶחָכָם כְּשִׂמְחָתוֹ עַל תִּקּוּן מִדּוֹתָיו, וּכְמַעֲשֶׂה שֶׁל הֶחָסִיד שֶׁשָּׁכַב בְּזָוִית הַסְּפִינָה וְלֹא הִקְפִּיד עַל זֶה שֶׁהִטִּיל עָלָיו הַשּׁוֹפְכִין, וְשָׂמֵחַ שִׂמְחָה גְּדוֹלָה כְּשֶׁהִרְגִּישׁ בְּנַפְשׁוֹ שֶׁלֹּא הִקְפִּיד"- הַחֲזוֹן אִישׁ/ אֱמוּנָה וּבִטָּחוֹן, ד, טו)