He had the arm. He had the height. He had the confidence and the charisma.

It was spring of 2009; Mark Sanchez had just wrapped up a spectacular season as the starting quarterback for the University of Southern California, leading the Trojans to a 12-1 record, culminating in a Rose Bowl victory. His stats were equally impressive: a 65.9 percent completion rate, and 34 touchdowns, the second most in Trojan history.

It was easy to see why the New York Jets were infatuated. Despite his relative inexperience (he had only played one season as a full-time starter at USC), Sanchez showed enough promise for the Jets to trade their 17th pick, their second-round selection and three players in order to select him, making Sanchez the fifth overall pick in the draft that year.

For the Super Bowl-starved franchise, the future suddenly looked bright. The Jets, it seemed, finally had a quarterback who could bring them all the way to a championship. He just had to live up to his potential.

Of course, that’s not how things panned out. Sanchez enjoyed a relatively successful two first seasons, leading the Jets to consecutive conference championships, but the team’s respectable record masked Sanchez’s mediocre stats: his completion percentage in his first years was a sub-par 54 percent, and his interceptions exceeded his touchdowns (33 to 29, plus 19 fumbles).

From there, things only got worse. The Jets ended the 2011 season with a tepid 8-8 record, and 2012 was a straight-up disaster, perhaps best encapsulated by the “butt-fumble,” in which a disoriented Sanchez collided with guard Brandon Moore’s raised rear end, fumbled the ball on impact, and could only watch as it was promptly picked up by the Patriots' defense and returned for a humiliating touchdown.

For all his promise, Sanchez had unequivocally failed to mature into a competent quarterback, much less an elite player capable of Tom Brady or Peyton Manning-like poise, leadership and ability. 

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How did the Jets get it so wrong?

Accurately predicting a quarterback’s success in the NFL is extremely difficult, says Todd McShay, a draft analyst and commentator for ESPN. Before a player is actually thrown into the brutally paced warzone that is professional football -- a world so removed from college football that teams don’t bother analyzing players’ collegiate reels -- it’s hard to predict how he will play, which is why the road is paved with so many Mark Sanchez’s (Tim Couch, Matt Leinart, Ryan Leaf), and why talented players are often drafted late (Tom Brady, Russell Wilson, Drew Brees).

One can rule out players based on obvious inefficiencies (clear-cut character issues, insufficient height, an inaccurate arm) but correctly identifying the magic combination of intangibles that will guarantee success is just too difficult. “Each team administers their own tests, they have their own psychologists…everyone is trying to crack the equation,” McShay says. “To date, no one has quite figured it out. It’s impossible to identify the perfect mental makeup because you just don’t know enough of the variables.”

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Venture capitalists face this problem, too.

Paul Lee is the managing partner of Vanedge Capital, a $136 million Canadian ($121 million US) fund based in Vancouver, Canada that invests in digital media companies. The fund was founded in May 2010, and since then, Lee estimates he’s evaluated thousands of companies. Over the years, he’s realized that “even more critical than what the company is doing are the people who are doing it. It’s simple: If you find really good people, they are going to find a way to succeed.”

But how do you identify those really good ones? It’s tricky. Lee emphasizes the difficulties of predicting a startup entrepreneur’s success. In fact, his language is eerily similar to McShay’s depiction of the unreliability of forecasting college quarterbacks’ NFL careers.

“I don’t know if we can ever determine if someone is exactly what I’m looking for, but we are looking for signs that they’re not,” Lee says. “It’s always easier to find the errors, how they are going to fail, than to figure out how they are going to succeed.” Like a quarterback, a startup entrepreneur needs to possess an extensive arsenal of tools, most of them intangible. There are simply too many variables to ever guarantee success. “You never know when there will be other competitors, or if something unexpected is going to happen. Guys who are really good at all this stuff, they find ways to navigate through.”

So what are the intangibles Lee looks for, difficult as they are to decipher beforehand? They mirror McShay’s criteria for elite quarterbacks: leadership, the ability to adroitly adapt to shifting circumstances, clarity of vision under pressure and work ethic.

While these are essential qualities (try starting a business without them), they are also prerequisites for success in most competitive fields.

What unifies quarterbacks and startup entrepreneurs is their grit -- an almost irrational unwillingness to accept failure, to back down or give up. Like a college quarterback attempting to make it in the NFL, the transition from a day job (even a high-ranking one) to entrepreneur is often rocky.

“Vince Lombardi liked to say ‘winning isn’t everything; it’s the only thing,’” says Dr. Stanley K. Ridgley, a former military intelligence officer for the U.S. Army and an assistant professor in the department of management at Drexel University’s LeBow College of Business, where he teaches strategic management and entrepreneurship. “This clangs against the senses of the average person who isn’t used to these declarative, unequivocal, unabashed pronouncements. Most of us are trained to be good losers. But this mentality is what separates entrepreneurs apart from the average person.”

Lee agrees. “We look for hunger,” he says. “People who have had a day job are fairly comfortable. They’re not paranoid enough: They can get another job, they’re not trying to prove anything, they don’t have a chip on their shoulder. If it doesn’t work out, they’ll just move on. They won’t think that their career or reputation is ruined.”

Related: What Entrepreneurs Can Learn From NFL Innovator Steve Sabol

Guard Louis Vasquez told NFL.com that Peyton Manning has no "off" switch at the Broncos' facility. "He'll stop a lot of receivers midway through the locker room," he told the outlet. "It seems like he's going about his business and all of a sudden he'll stop and ask a question about a route or even with us, a question about protection. Usually when guys are in the locker room, you stop to take a break. But his mind is always going.”

For the successful quarterback, during the season, football is his life. Whenever there’s an off moment, he turns to the tape. If he’s going to establish himself as a starting quarterback, this is the only way to do it. There’s no shortcut. 

There’s no shortcut for entrepreneurs, either. “It takes a very special person to be an early stage entrepreneur because in addition to being passionate about your idea and wanting to take it to market, you have to really understand what you’re signing yourself up for,” says George Deeb, a two time startup entrepreneur and now the managing partner of Red Rocket, a Chicago-based strategic consulting and financial advisory firm. “The long hours around the clock, the unknowns, the craziness, all the ebbs and flows… It’s very glamorous to say you just launched as startup, but to actually do it? It’s a crazy amount of work.”

If your business is your life, you'd better enjoy the work, preparation and sheer effort that go into starting something. Because the odds won’t be in your favor. “Simply put,” says Deeb, “there’s going to be a lot more bad times then good for most startups.” Maintaining a level of optimism that borders on lunacy (at least from the outside) can be helpful.

In his book Collision Low Crossers (Little Brown & Company, 2013), which chronicles his year spent with the Jets, Nicholas Dawidoff writes that despite the frequent lopsidedness of the scoreboard, the Jets' head coach Rex Ryan truly expected to win every game up until the final whistle. He believed that for the season, too, utterly convinced his team would be at the Super Bowl despite the piled up losses.

From the start, the Jets faced 31 other teams also trying to claw their way to the championship. Startup entrepreneurs face even more discouraging odds. Just getting funding is a strenuous battle in itself -- out of over a thousand companies, Lee has funded 12 of them. That’s a pretty grim percentage.

And it’s no walk in the park for startups that do receive even substantial venture capital; failure is still common, success very rare. Shikhar Ghosh, a senior lecturer at Harvard Business School, told The Wall Street Journal that about three-quarters of venture-backed firms in the U.S. don't return investors' capital. Three to four out of every 10 belly flop, liquidating all assets.

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With this in mind, can you take the heat? “Entrepreneurship is about being able to make decisions that are cool and collected under conditions of intense stress,” Dr. Ridgley says. “It certainly isn’t for everyone. You have to have this incredible belief in yourself coupled with an honest and clear-eyed assessment of your idea’s actual value."

Because entrepreneurship is a highly visible venture fraught with risk and studded with failure, there will always be jeers, naysayers, and thoughtful analyses of why a new venture is going to fail. Like a quarterback, an entrepreneur is publicly scrutinized, will be humiliated in the press for every misstep or “butt fumble”. Of quarterbacks, McShay says “You’re going to make mistakes… if you get your ass handed to you, are you able to bounce back up and deal with the pain and play at a high level?”

You can have the right degree, a high IQ, buckets of charm, all the right skills on paper, but if the answer is no, you probably shouldn’t be a quarterback, and you probably shouldn’t be an entrepreneur. Get a day job.

Because starting your own business, as Lee likes to say, is “a whole different game.”