Shelomo HaMelekh (King Solomon) famously [wrote][1] in his 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][2], [Perush HaGR"A][3], [Perush Rabbe'inu Yonah][4] and [Perush HaMaLBI"M][5] and have not seen anyone ask/answer: why ***seven*** and not another number?

  [1]: http://chabad.org/16395#v=16&showrashi=true
  [2]: http://hebrewbooks.org/pdfpager.aspx?req=14259&st=&pgnum=149
  [3]: http://hebrewbooks.org/pdfpager.aspx?req=14229&st=&pgnum=141
  [4]: http://hebrewbooks.org/pdfpager.aspx?req=39300&st=&pgnum=144
  [5]: https://he.wikisource.org/wiki/%D7%9E%D7%9C%D7%91%D7%99%22%D7%9D_%D7%A2%D7%9C_%D7%9E%D7%A9%D7%9C%D7%99_%D7%9B%D7%93#.D7.A4.D7.A1.D7.95.D7.A7_.D7.98.D7.96_.28.D7.9B.D7.9C_.D7.94.D7.A4.D7.A8.D7.A7.29.28.D7.9B.D7.9C_.D7.94.D7.A4.D7.A1.D7.95.D7.A7.29