Reb Yisrael Salanter teaches in his famous Iggeret that a person must take stock of their character traits and history — self-knowledge rooted in honest reflection on one's past is the indispensable foundation for moral transformation.
עַתָּה, בְּכָל הָאֳפָנִים אֲשֶׁר יִתְיַצֵּב הָאָדָם, מַה יַּעֲשֶׂה, יוֹם הַמָּוֶת מִכֹּל מְכֻסֶּה, פִּתְאוֹם יָבוֹא, וְהָאֱלֹהִים יִפְקֹד אֶת כָּל מַעֲשֶׂה אֲשֶׁר עָשָׂה מִסְפַּר מִפְקַד יְמֵי חַיָּיו, אַחַת מֵהֶן לֹא נֶעְדָּרָה, וּמַר מִמָּוֶת תִּהְיֶה הָאַחֲרִית בְּאֵין מָנוֹס וּמִפְלָט לְהִנָּצֵל. הוּא מַאֲמַר הַכָּתוּב (קֹהֶלֶת ט', ד') כִּי מִי אֲשֶׁר יְחֻבַּר אֶל כָּל הַחַיִּים יֵשׁ בִּטָּחוֹן, כִּי לְכֶלֶב חַי (כִּדְרָשַׁת רַבּוֹתֵינוּ זַ"ל) הוּא טוֹב מִן הָאַרְיֵה הַמֵּת, כִּדְרָשַׁת רַבּוֹתֵינוּ זַ"ל (בַּיַּלְקוּט בִּמְקוֹמוֹ), שֶׁכָּל זְמַן שֶׁאָדָם חַי יֵשׁ לוֹ בִּטָּחוֹן וְתִקְוָה לַעֲשׂוֹת תְּשׁוּבָה וְכֵיוָן שֶׁמֵּת אָבְדָה תִּקְוָתוֹ כוּ': אִי לָזֹאת, כָּל עוֹד נִשְׁמָתֵנוּ בְּקִרְבֵּנוּ, נְמַהֵר נְחִישָׁה לְפַלֵּס דַּרְכֵּנוּ לְטוֹב, אָכֵן עַל יְדֵי אֶבֶן הַנֶּגֶף יִרַט הַדֶּרֶךְ לְנֶגְדֵּנוּ. לֹא נֶחֱרַד מִיּוֹם הַמִּיתָה גַּם אִם בְּפִינוּ נַזְכִּירֵהוּ, כְּמַאֲמַר רַבּוֹתֵינוּ זַ"ל (שַׁבָּת לא:) שֶׁמָּא תֹּאמַר שִׁכְחָה הִיא כוּ,' גַּם אִם עֵינֵינוּ רוֹאוֹת מִיתַת בְּנֵי אָדָם כָּמוֹנוּ, לֹא תִּתֵּן עֹז בְּנַפְשֵׁנוּ לָשׁוּב בְּכָל לֵב לְבוֹרְאֵנוּ, אֲשֶׁר לַסּוֹף נָבוֹא לְפָנָיו לְמִשְׁפָּט וְיִתְוַכַּח עִמָּנוּ עַל כָּל רֹעַ מִפְעָלֵינוּ, הֵפֶךְ מַאֲמַר הַכָּתוּב (קֹהֶלֶת ז', ב') טוֹב לָלֶכֶת אֶל בֵּית אָבֵל מִלֶּכֶת אֶל בֵּית הַמִּשְׁתֶּה בַּאֲשֶׁר הוּא סוֹף כָּל הָאָדָם וְהַחַי יִתֵּן אֶל לִבּוֹ. אֵין זֹאת, כִּי אִם רִבּוּי הָעֲוֹנוֹת שֶׁטִּמְטְמוּ לִבֵּנוּ וַיְהִי לְאֶבֶן, כִּדְרָשַׁת חֲכָמֵינוּ זַ"ל (יוֹמָא ל"ט) עַל הַפָּסוּק (וַיִּקְרָא י"א) וְלֹא תִּטָּמְאוּ בָּהֶם וְנִטְמְתֶם בָּם אַל תִּקְרֵי וְנִטְמֵאתֶם אֶלָּא וְנִטַּמְטֵם כוּ'. וְלָכֵן גַּם עֲוֹנוֹתֵינוּ נִסְתָּרִים מִלְּפָנֵינוּ, וְלֹא נַרְגִּישׁ בַּהֶם בִּמְהֵרָה, כְּמַאֲמַר רַבּוֹתֵינוּ זַ"ל (קִדּוּשִׁין מ') כֵּיוָן שֶׁעָבַר אָדָם עֲבֵרַה וְשָׁנָה כוּ' נַעֲשֵׂית לוֹ כְּהֶתֵּר, וְהֵן מְסַבְּבִים אוֹתָנוּ לְיוֹם הַדִּין, כְּמַאֲמַר רַבּוֹתֵינוּ זַ"ל (עֲבוֹדָה־זָרָה י"ח) עֲוֹנוֹת שֶׁאָדָם דָּשׁ בַּעֲקֵבָיו כוּ' הֵן מְסַבְּבִין כוּ'. עַתָּה הַאִם אָבְדָה תִּקְוָתֵנוּ חַס וְחָלִילָה, אֵין מָזוֹר לָנוּ חָלִילָה:
Now, in whatever circumstances in which a person is situated, what shall he do? The day of death is hidden from everyone. It will come suddenly, and God will remember every act he did in accordance with the number of the recorded days of his life. Not one of them is omitted. This end will be more bitter than death with no escape or refuge to save him. This is what the verse states (Eccl. 9:4): “For he who is reckoned among the living can be secure; for a live dog is better than a dead lion.” As interpreted by our Rabbis, of blessed memory (in the Yalkut on that verse), as long as a person is alive, he has the security and hope that he can repent, but once he dies, his hope is lost…. In light of this, as long as our soul is still in us, we should quickly hasten to set our course toward the good. However, there is an obstacle blocking the road to us. We do not tremble at the day of death, even if we pay lip service to it. As our Rabbis, of blessed memory, say (Shabbat 31b): “Lest you think it is a matter of their [evil men] forgetting [the day of death]...” Even if our eyes see the death of a person just like us, it does not embolden our souls to return to our Creator with a full heart – notwithstanding that in the end we will come before Him for judgment and He will contend with us on all our evil activities. This [indifference to our death] is the opposite of Scripture’s statement (Eccl. 7:2): “It is better to go to a house of mourning than go to a house of festivity, for this death is the end of every man and the one who lives should take it to heart.” This is only because our many sins have dulled our heart and turned it into stone. As our Sages, of blessed memory, expound (Yoma 39a), on the verse (Lev. 11:43): “‘Velo tit’amu vahem, venitmeitem bam’; do not read venitmeitem [you shall become unclean], but venitamtem [you shall become dulled]....” Therefore, even our sins are hidden from us and we do not feel them readily. As our Rabbis, of blessed memory, say (Kiddushin 40a): “Once a person does a sin and then repeats it…it becomes [in his mind] as if [the act is] permitted.” Yet these bad acts beset us on the day of judgment. As our Rabbis, of blessed memory, say (Avoda Zara 18a): “Sins that a person tramples underfoot...beset him [on the day of judgment]....” So have we lost hope, God forbid? Is there no healing for us, God forbid?