Why are QBs so difficult to assess?

They can tell their stories now with a sense of deep satisfaction, as men who bronzed their NFL reputations by finding three of the greatest quarterbacks in a generation should.

Ron Wolf, soaking up retirement in South Florida, can recall standing in front of the Green Bay Packers' board of directors, telling them the player they would get from the Atlanta Falcons in return for a first-round pick in 1992 -- an unbridled 22-year-old named Brett Favre -- was going to have the same effect on the franchise that Lou Gehrig did on the New York Yankees.

Minnesota Vikings offensive coordinator Norv Turner can reminisce about the preternatural sense of anticipation he saw in a prolific Purdue quarterback named Drew Brees and remember how sure it made Turner (then the San Diego Chargers' offensive coordinator) that Brees, who barely measured 6-foot, would overcome whatever obstacles stood in his way if the Chargers picked him in the 2001 draft.

And former Indianapolis Colts general manager Bill Polian, who now works as an ESPN analyst, can think back to a mid-March workout in 1998 with a tenacious Tennessee quarterback named Peyton Manning and how it cemented a choice that simultaneously shot the Colts toward success and steered them away from disaster.

All three men have a sense of certitude about what they saw in each quarterback, and all three are rightfully proud they were correct. But instead of sounding like card-counting savants who took down Las Vegas casinos with ease, all three are grateful for the chance to have been right on a decision that could benefit them so much.

"That's why it's such a unique position," Wolf said. "For anybody to think they have a handle on it, if anybody's telling you that, they're full of crap."

For all the gigabytes of statistical research, thousands of scouting man hours and hundreds of interview questions spent on finding a franchise quarterback, the game's most important personnel task remains a highly calculated gamble. Get it right, and you'll be living large for years. Get it wrong, and expect to be fired, or at least right back at the table in a couple of years, tossing a new set of chips at a number you're hoping will come through for you this time.

There's disagreement among NFL general managers about whether quarterback is a more difficult position to evaluate than any other, but there is no debate about which position has the shortest supply of great players. In an era in which quarterback play might be more central to a club's success than ever, NFL teams can't help themselves from coming right back to try their hand again.

From 1960 to 1979, 59 quarterbacks were taken in the first two rounds of the draft. That total spiked to 66 from 1980 to 1999, and since the year 2000, there have already been 53 selected in the first two rounds, with four or five more likely to go this year.

But most of the teams that pick a quarterback early in this year's draft should know there's a probability their bet won't come through. Of the 137 quarterbacks taken in the first two rounds of the draft since the 1970 AFL-NFL merger, only 54 (39.4 percent) turned out to be five-year starters, according to Pro Football Reference.

The riches that await the one or two lucky winners this spring, though, are significant: Seven of the past nine Super Bowls have been won by teams starting a first-round pick at quarterback. The other two winning quarterbacks, Brees and Russell Wilson, went in the second and third rounds, respectively. One or two correct decisions can buy decades of success for a franchise: The Packers have as many championships as losing seasons (two) in their 22 years with Favre and Aaron Rodgers, and the Colts have been to the playoffs 13 times in the 15 years they've had a healthy Manning or Andrew Luck.

For each of those teams, though, there are others who have been snakebit: The Vikings, Cleveland Browns and Oakland Raiders have gone decades without a true franchise quarterback. Others, such as the Chicago Bears, Dallas Cowboys and Detroit Lions, are caught in the middle, with a quarterback good enough to put up big numbers but so far unable to deliver consistent success.

The necessity of the position will keep teams coming back to the table, hoping the homework they've done will make their next bet pay off.

"Teams that don't have a franchise guy are always going to be doing that," Vikings general manager Rick Spielman said. "You have to do everything you possibly can to try to get that right person."

Identifying subtle traits can be difficult

Those who say the quarterback position is more difficult to assess than any other, such as Atlanta Falcons GM Thomas Dimitroff and 49ers GM Trent Baalke, point to the myriad roles a quarterback must play: leader, tactician, manager, athlete, passer, liaison and counselor among them, none less critical than the other.

It's like trying to identify the traits of a great CEO -- is the pragmatism of Warren Buffett better than the innovation of Steve Jobs? -- and general managers are tasked with projecting all of it in 22-year-olds.

"It's a guy who can make all the throws, can win under pressure, operate the offense at an exceptionally high level, lead you back when it looks hopeless and win games you have no business winning," said Polian, reciting with no sarcasm the list of traits necessarily present in a great quarterback. "It's pretty obvious."

The process of finding those traits in draft-eligible quarterbacks can be murky because of how difficult they are to project. Polian and current Colts GM Ryan Grigson (who drafted Luck to succeed Manning) both place a high emphasis on a quarterback's ability to make throws under duress, which can be hard to see in college when pass-rushers aren't as effective and many QBs don't spend much time under center.

"You're asking a lot, and it's hard to figure out as you're scouting college guys who aren't running the same scheme," said ESPN Insider Matt Williamson, a former NFL scout. "They haven't run a three-, five-, or seven-step drop with J.J. Watt bearing down on them."

Turner and Packers coach Mike McCarthy also stress the importance of a quarterback's ability to quickly digest offensive concepts and his anticipatory skills -- to close his eyes and see how a defense will react as a play unfolds. As the Vikings evaluate quarterbacks this year, Turner will put them through the same exercise he did with Brees, in which the coordinator stood at a whiteboard, diagrammed dozens of plays with different personnel groupings and protection schemes and then sat down and asked the quarterback to go through a handful of the plays he'd just learned. McCarthy will use a similar process, firing impromptu quiz questions on offensive plays and defensive tactics as he watches film with quarterbacks.

"It's a quality that's really critical," Turner said. "I played in college with one of the best and got to watch him play his entire career: Dan Fouts. You'd watch some of the times where he'd throw the ball, how he'd throw it; it's remarkable. It's a quality the best guys have. Troy Aikman. Brad Johnson was outstanding. Drew has great anticipation, great understanding. I don't think you're going to have consistent success if that's not something that's in your nature."

Teams administer numerous personality tests and learning assessments and get all the outside help they can on how to find what makes a player tick; the Vikings, for example, talk to psychologists and corporate headhunters to fine-tune their interview process. They, and other teams, keep a file of every data point they can find on a player, from height and weight to Myers-Briggs personality type. If there's a precedent for a player of similar attributes being successful in the NFL, all the better. For many, the trick is not to let the subtler traits of quarterbacking get obscured by a big arm or ideal stature.

"A lot of times, people overemphasize certain skills," Grigson said. "Sometimes you'll overemphasize arm strength, but if a guy can't read a defense, he can't use that arm. And then sometimes, you'll overemphasize athletic ability, but a guy might not have the top arm strength or the release quickness or the size. A lot of things have to line up."

Short quarterbacks no longer overlooked

Thanks largely to Brees and Wilson, though, height -- or a lack of it -- isn't a non-starter for quarterbacks anymore.

Wilson, who threw 33 touchdown passes as a senior at Wisconsin in 2011 -- the No. 2 single-season mark in Big Ten history behind Brees, who threw 39 for Purdue in 1998 -- came into the draft drawing rave reviews for just about everything but his height.

"You'd put on the tape, and [his throws were] like, pinpoint, no matter where he was at," Grigson said. "That's before he's had any NFL coaching, before he's really been seasoned at the position. [The reason he fell to the third round] was height, period."

But now the 5-foot-11 Wilson has a Super Bowl title to his name and is likely a year or two away from a major contract extension. He's done plenty to reduce the stigma associated with short quarterbacks, and the 5-foot-11¾ Johnny Manziel, who could be one of the first picks in the draft this spring, is all but a lock to be the first QB under 6-foot to go in the first two rounds of the draft since Ted Marchibroda in 1953.

The fact that the height issue dogged Wilson at all might have been an example of groupthink gone overboard; Grigson recalled watching Wilson's tape and noticing how good the quarterback was at finding passing lanes and avoiding batted throws. Brees had learned to play the same way at Purdue, and both of them have helped broaden the spectrum of the types of quarterbacks that are taken seriously in the NFL.

"I think it was Johnny that said Russell had opened the door for him and guys like him. That's true," Seahawks coach Pete Carroll said. "Prior to the last couple of years, the general thinking was that a guy of Russell's stature couldn't play, which obviously is wrong. It's just wrong. Anybody who said that is wrong. But not everybody who is 5-11½ can play quarterback. You've got to be a great football player. All the elements that make up Russell make him very, very unique regardless of how tall he is."

Said Polian: "They compensate for it. [New Orleans Saints coach] Sean Payton has found ways to compensate for it. Drew and Russell were the same guy in terms of their demeanor and what they brought to the game, their work ethic, their dedication. Their leadership is 24-karat gold."

Mistakes will keep happening, but teams will keep trying

The exacting nature of the quarterback position means there are going to be fewer players such as Brees, Rodgers, Manning or Tom Brady than there are teams that want them.

That gap between supply and demand, Wolf believes, will always have teams grasping for a solution.

"When I started following the position [in 1953], there were 12 teams in the league. Seven had quarterbacks and five didn't," he said. "Now, there are more than 16 teams that don't have quarterbacks -- I'm talking about the real deal here, guys that have a chance to move on up. I'm not sure anybody's got that key that can unlock what it takes. You don't know what's inside a guy until you have that guy at your place."

There is perhaps no better example of that than the quarterback the Colts didn't take in 1998: Ryan Leaf, whom some believed was in a dead heat with Manning and whom the Chargers took with the second overall pick. Leaf was out of San Diego by 2001, out of the league by 2002 and is currently serving a prison sentence after pleading guilty to felony burglary and drug possession in Montana in 2012.

Leaf's character issues were evident to the Colts, Polian said, but some teams might have been swayed by his talent, believing they could correct his reputation for questionable off-field behavior.

Other cautionary tales garner fewer headlines, but are no less detrimental to a team's progress. The Jaguars and Vikings could both wind up drafting quarterbacks in the top eight picks again this May, three years after they took Blaine Gabbert and Christian Ponder with the 10th and 12th overall picks, respectively. The effects of misjudging a quarterback are less costly now, thanks to the 2011 collective bargaining agreement that capped rookie contracts, but a wasted first-round pick is still a major mistake in roster construction.

After the Seahawks and Philadelphia Eagles hit on a pair of third-round picks in 2012 with Wilson and Nick Foles, more teams might try to find a quarterback later in the draft, using a first-round pick to fill another need while hoping they can mold a midround selection.

"I think you have to see the potential," Hall of Fame quarterback and Denver Broncos general manager John Elway said. "You have to have the raw potential of the arm strength and the ability to move around and to process information. Those are the three things you try to find out about in a quarterback. It's up to us in that point in time to coach them and see if they can mature and become the player you want them to be at the position. You have to have that ability, first, and then hopefully we can get it out of you."

That strategy, though, is only a different version of the same bet with slightly lower stakes. When looking for quarterbacks, everybody is gambling on something, whether it's their ability to project greatness, a coach's effectiveness at matching a player with a scheme, or a passer's propensity to learn and his drive to be the best.

The payoff -- Super Bowls, contract extensions for both player and evaluator, a long period of stability at the most important position in sports -- is too vast for teams not to keep trying, mistakes and all. But even those who have reaped the greatest returns from their quarterback picks know how fortunate they are to be remembered for their successes more than they are held responsible for their mistakes.

"You'd like to think you're always right," Turner said. "But some guys handle this level of competition better than others. This game is faster; it's more physical; it's more competitive. Guys don't get open by as much. They don't stay open as long. Some guys, you see things in them, and you say, 'Hey, I think this guy has what it takes,' and it doesn't transfer the way you'd expect it to. I think that's happened for anybody who's evaluating players in this league."

Said Wolf: "If you had a key to that position, you could retire and buy an island. For every one you get correct, you get six, seven, eight or nine more incorrect. People try to make it a science. There's no science involved here. You've got to have a little luck."

ESPN NFL Nation reporters Rob Demovsky, Jeff Legwold and Michael Rothstein contributed to this report.