Many college football coaches, moonlighting as expert mathematicians, subscribe to the equation that two quarterbacks actually equals zero quarterbacks.
Others who attempt to use quarterback rotations end up with stagnant offenses. Quarterback competitions can be beneficial, but they also often divide locker rooms and lead to transfers. There are rare cases when a two-quarterback system works, and Northwestern appears to have found the formula.
The Wildcats won 10 games last season while rotating Kain Colter and Trevor Siemian at quarterback. Although Colter started 12 of the 13 games and finished second on the team in both carries (170) and rushing yards (894), Siemian had more completions (128), pass attempts (218) and pass yards (1,312).
The offense wasn't a juggernaut -- 42nd nationally in scoring, 64th in yards -- and the rotation caused a midseason identity crisis, but Northwestern worked through it to have its most successful season under coach Pat Fitzgerald.
Both Colter and Siemian return for the 2013 campaign, and the bar has been raised.
"I believe we have two quarterbacks who can lead us to a Big Ten championship," Fitzgerald told ESPN.com before spring practice.
Why does Northwestern's two-quarterback system seem to work when many others fail?
It starts with acceptance.
As recent history shows, playing two quarterbacks is more of a necessity than a luxury in Northwestern's offense. The team has used multiple starting quarterbacks in each of the past three seasons and four times in the past five.
The nature of Northwestern's spread offense, which requires the quarterback to run and exposes him to injury, makes it essential to have multiple options.
"We'll always have to play our No. 2 quarterback no matter what because [the starter] is going to get dinged up," offensive coordinator Mick McCall said. "It's going to happen."
No player understands this more than Colter, who burned his redshirt late in the 2010 season because star quarterback Dan Persa ruptured his Achilles' tendon. Colter opened 2011 as the starter because of Persa's injury and shared time with Persa before rotating with Siemian last fall.
Colter's unique skill set -- he recorded 43 receptions in 2011 and might be the team's top receiver and best overall athlete -- increases McCall's flexibility at the quarterback spot. Siemian, meanwhile, has the stronger throwing arm of the two.
"It’d be stupid to say he’s not going to play," Colter said, referring to Siemian. "I think we both showed that we’re both going to play this year. It’s been a two-quarterback system ever since I’ve been here. Do I want the opportunity? Yeah. And I’ve had the opportunity in games where I’ve been the only quarterback, but I also feel at some point, I'm one of the best receivers we have on the field and one of the best running backs, so we have to get me in different areas."
Another key to the rotation is the strong friendship between Colter and Siemian. They both arrived at Northwestern in 2010 and studied the playbook together. Both were on track to redshirt before Persa's injury, which thrust Colter into the fire.
Siemian backed up Colter at times during the 2011 season before moving into more of a co-starter role last fall.
"We're two pretty unselfish guys," Siemian said. "A lot of times at places, I’ve heard you get a quarterback competition or you get two guys buying time, and that kind of divides the team in two. We're all in this together. That's just part of the culture here as a program. It's not like Kain and I are that special, but we're all going for a Big Ten championship and a Rose Bowl."
Added Colter: "We've been through this whole thing together, all the offensive changes, all the quarterback changes. He's always helped me out and I try to help him out in any way that I can."
Colter's and Siemian's skills seemed to complement each other well for much of 2012.
As Northwestern transitioned to more of a run-based offense, Colter and running back Venric Mark shined in the zone-read game, and Colter's scrambling skills converted numerous third downs. Siemian showed off his arm on downfield throws and threaded the ball into tight windows. And while Colter didn't play nearly as much receiver because of the injury risk, he and Siemian connected nine times for 131 yards in a win against Indiana (Colter also had 161 rush yards and four touchdowns as a quarterback in the game).
"He’s one of our better receivers when he lines up out there, so for me, selfishly, I like it," Siemian said. "But then again, he's so dangerous when he lines up at quarterback."
Colter is working strictly as a quarterback in spring practice, but the door hasn't been closed to him playing other positions in the fall.
"We need him to get better at playing quarterback," McCall said. "As time goes on, there's always going to be a possibility of he and Trevor playing together on the same snap. That puts pressure on defenses. We can change some things up, they don't know actually what’s going on, it simplifies what they do. There's always going to be that opportunity as we go forward."
Colter's flexibility can keep defenses off balance, which Northwestern struggled to do with its rotation midway through the 2012 season. Offensive production dropped off in early October as Colter handled most run plays while Siemian was brought in for obvious third-and-long passing situations.
In late October, Colter questioned the unit's identity in an interview with ESPN.com, saying Northwestern had to fully commit to an option-based attack. Several days later, Colter and Mark combined for 328 rush yards in a win against Iowa.
"We know exactly who we are," Fitzgerald said. "The bottom line is we want to win, and we're going to do what’s best for the team first. Fans want to say, 'Why don't we throw it better with Kain, and why don't we run it better when Trevor’s in there?' Keep talking all you want, but the bottom line is we won the game. It's one of those situations where you want to play to guys' strengths, but you also don't want to be predictable.
"That's where the balancing act is."
There's also a balance with leadership that Colter and Siemian intend to reach in 2013. Colter, a co-captain in 2012, almost certainly will retain the title as a senior this fall.
He made his desire clear in a recent interview, saying, "No matter where I’m at [on the field], I'm going to be the leader on this team."
It's not an affront to Siemian, who doesn't take it that way.
"I'm a quarterback, so it'd be foolish for me to say I'm not a leader," Siemian said. "But Kain's a tremendous leader. He's done well leading our offense, but I have a leadership role on this team, too."
The Big Ten hasn't had a team with a true quarterback rotation win a league title in recent years. Northwestern hopes to change that this fall.