Without a doubt, every game matters.
With few exceptions, a single game doesn't define a season. A great victory can be deflated by an upset the next weekend, while a crushing defeat can be redeemed by an inspired effort later in the season.
While the Pac-12's national title contenders -- we won't name names -- need to win every game (or just about), before each season you can point to a stretch of games on the schedule that appears defining for every team. In terms of a team's goals, that stretch is most critical.
We've defined a "key stretch" as three games, though we will allow for those three games to come among four.
Key stretch: Nov. 13 California, Nov. 22 at UCLA, Nov. 29 Notre Dame
Why it's critical: We could have included the visit to Washington State on Nov. 1 that precedes this troika. The Cougars, after all, upset the Trojans last season, so USC should be plenty motivated to get revenge for an embarrassing loss in front of booing fans in the Coliseum who were chanting for Lane Kiffin's head on a platter last September. And November dates in Pullman can be pretty iffy weather-wise. But really, this is about the last two games against archrivals. Cal is included because it would be pretty humiliating for new coach Steve Sarkisian to lose at home to the rebuilding Golden Bears, thereby inviting media to proclaim that the Trojans were "looking ahead."
There simply is no way for Sarkisian to have a successful first season if he loses to both UCLA and Notre Dame. And beating both would make up for just about everything bad that could happen in advance of these two games.
A third consecutive loss to UCLA, the South Division favorite, would give USC a true losing streak in the series. It would recall the dark period from 1991 to 1998 for Trojans fans, when the Bruins won eight in a row in the series.
Beating UCLA is more important than beating Notre Dame, but at least the Trojans figure to be underdogs in the Rose Bowl.
Ending Sarkisian's first year with a loss at home to the Fighting Irish wouldn't exactly go over well either, but it would be a particularly sour pill if it means the regular season concludes with consecutive painful losses. Suffice it to say, Sark's honeymoon would end quickly.
Other key stretches: