כִּי אֶלֶף שָׁנִים בְּעֵינֶיךָ כְּיוֹם אֶתְמוֹל כִּי יַעֲבֹר וְאַשְׁמוּרָה בַלָּיְלָה
For a thousand years are in Your sight like a day gone by and like a watch of the night.
The Radak explains that a human should never be lulled into a false sense of importance by his relative greatness compared to other mortals. Even if a person were to live a thousand years, his end is the same as everyone else’s and once his life is over, it’s like a day gone by regardless of its length. Furthermore, in G-d’s sight, all of our lives – even the longest – are the merest blip in time.