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For a righteous man can fall seven times and rise - why seven?

Shelomo HaMelekh (King Solomon) famously wrote in Mishle'i 24:16 (Proverbs):

כִּי שֶׁבַע יִפּוֹל צַדִּיק וָקָם וּרְשָׁעִים יִכָּשְׁלוּ בְרָעָה

For a righteous man can fall seven times and rise, but the wicked shall stumble upon evil.

I've looked through Miqra'ot Gedolot, Perush HaGR"A, Perush Rabbe'inu Yonah and Perush HaMaLBI"M and have not seen anyone ask/answer: why seven and not another number?