Mishnah Sanhedrin
Mishnah Sanhedrin 4:5
The Mishnah teaches that each person is obligated to say 'the world was created for my sake,' because unlike a king who stamps many coins from one mold and they are all identical, God stamps every person from the seal of Adam and not one is like another.
וּלְהַגִּיד גְּדֻלָּתוֹ שֶׁל הַקָּדוֹשׁ בָּרוּךְ הוּא, שֶׁאָדָם טוֹבֵעַ כַּמָּה מַטְבְּעוֹת בְּחוֹתָם אֶחָד וְכֻלָּן דּוֹמִין זֶה לָזֶה, וּמֶלֶךְ מַלְכֵי הַמְּלָכִים הַקָּדוֹשׁ בָּרוּךְ הוּא טָבַע כָּל אָדָם בְּחוֹתָמוֹ שֶׁל אָדָם הָרִאשׁוֹן וְאֵין אֶחָד מֵהֶן דּוֹמֶה לַחֲבֵרוֹ. לְפִיכָךְ כָּל אֶחָד וְאֶחָד חַיָּב לוֹמַר, בִּשְׁבִילִי נִבְרָא הָעוֹלָם.
The court says to the witnesses: And perhaps you will say: Why would we want this trouble? Perhaps it would be better not to testify at all. But be aware, as is it not already stated: “And he being a witness, whether he has seen or known, if he does not utter it, then he shall bear his iniquity” (Leviticus 5:1)?
Why it matters — The definitive Talmudic statement on the absolute uniqueness of every individual — no two people are alike — which grounds the idea of a unique personal mission.