GREEN BAY – Three years ago, Alex Green was The Man.

Not only was he the star running back for a Football Bowl Subdivision (formerly Division I) program at the University of Hawaii, he could lay claim to an entire island as his playground.

Drafted by the Green Bay Packers in the third round of the 2011 draft, the running back learned a quick lesson in the pecking order. A National Football League locker room is filled with alpha dogs, The Man at each alma mater represented.

Of all the transitions between professional football and the college game a young player has to make, that is one of the most interesting.

"It's a business now," Green said. "Coaches have to keep their job as well as we do, so they're going to play the best players. Our job is to know what we're doing mentally as well as what we're doing physically. That's probably the biggest transition – there's not a lot of room for error here. If you make too many mistakes, you can't play. If you don't play, you'll be out of a job. It's a little, tough transition. I picked that up coming from last year so once the (rookies) start picking it up it makes more sense almost and there's a little bit more urgency."

The second-year running back was reminded of that again first had a couple weeks into camp when the Packers signed veteran Cedric Benson.

Benson, a former top 5 pick of the Chicago Bears, is coming off three consecutive 1,000-yard seasons. The move immediately began to redefine the roles of the backs already on the roster.

Such a change – as well as the level of competition – can also bring a new word into the vocabulary of a young player: Doubt.

Since Pop Warner, every player in an NFL training camp has been one of the biggest, strongest, or fastest on the field. They are singled out as special at an early age, with coaches from high school to college recruiting them to their schools, saying they are the key to the next championship.

That continues on to draft day, where a team determines they want you over the next guy. Same goes for those undrafted free agents. At some level, a player is picked over another, deemed to have greater qualities than the next.

But once in that locker room, on that practice field, that stops. There are others that have more stature – physically, in the coach's eyes, and in the wallet.

It's a shock to the system.

"You come from a college where you pretty much know it all and that's why you're in the position you're in now playing in the NFL," said linebacker Terrell Manning, a rookie out of North Carolina State.

"But here, it's completely different. Completely different than what you thought you knew and a completely different speed than what you're playing in college. I definitely had a shock when I came in because I was so used to being 'that guy.' Here, you know, you gotta wait a while. You definitely have to go through a few battles before you can be that guy."

The NFL is often cited as an acronym for "Not For Long," and the average career is only between three to six years.

Talent and injury play big roles, but sometimes the ability to get over that self-doubt is just as important. The only real similar experience a player can draw on is their first year out of high school.

"There's a lot similar to being a freshman in college and a rookie in the NFL," Manning said. "You still go through that phase of OK, am I made for this game? Is this what I'm supposed to be doing? There are days when you question yourself. But at the same time you've got have that mentality to where OK, you're getting paid to do this, you're a professional athlete and they believe in you, so believe in yourself. I had that day. I had that day. I think I'm done with them now so now it's about just looking forward to the future and just trying to be a part of this team."

Those doubts may creep in naturally, but they need to be excised quickly - patience is fleeting at the professional level.

"When you're in college, you can mess up and everything and you're on scholarship, so it's not as bad and they'll teach you up on it," Green said. "Here, you gotta come in pretty much knowing the majority of what you're supposed to do – that's why you're drafted or brought in (as a free agent). Making a mistake is crucial to your job."

Tonight's pre-season finale against Kansas City is the final day for those making these adjustments, for those trying to eliminate mistakes, to prove they belong in the Packers locker room.

On Friday, 22 players will be cut preparation for the regular season. It's the continuation of never ending cycle. Some of the first or second-year players will open the season against the 49ers on Sept. 9, others will be told to go home. In eight months, a new draft class will be welcomed in, and it begins again.