Most people felt that Tom Brady had nothing left to prove about three or four championships ago, but the star quarterback continues to find ways to stay motivated. Had the 2007 New England Patriots completed their perfect season, that might not have been the case.

Episode 4 of the ESPN+ documentary “Man in the Arena,” which will air next week but was previewed by NESN’s Zack Cox, covers the 2007 Patriots. In the episode, Brady makes a surprising revelation about how New England’s loss in Super Bowl XLII shaped his career. Had the Patriots won and completed their 19-0 season, Brady says he may have retired a lot sooner.