Entering your 10th, 11th or 12th NFL season at quarterback for the same franchise is an exceptional feat. It also often means that fixations boil.
Rather than simply being a quarterback under fire in America's most popular sport, you are an older hand in an inferno.
Brady enters his 10th season with the Patriots, rebounding from major knee surgery that ruined his 2008 slate. McNabb enters his 11th season with the Eagles with a re-built offensive line, new passing weapons and a backup quarterback in Michael Vick who could become an Eagles focus. And Manning strides into his 12th season with the Colts with a new head coach, a new offensive coordinator and some new receivers.
One of the splendid advantages of featuring a veteran quarterback is the overall experience he offers, the sage, in-game decision-making he can provide and a calmness and professionalism that he can exude team-wide.
The downside can be that familiarity breeds boredom.
That the voice is tired and the body is, too. An older quarterback has to keep proving he can still survive big hits and tough conditions, particularly bitterly cold weather.
He has to constantly prove that the mind and body are not only still fresh and engaged but also capable and willing.
NFL coaches and personnel executives insist that their sport is a "young man's game."
Brady is 32. McNabb turns 32 in November. Manning is 33.
"Those aren't exactly rocking-chair-ages for quarterbacks, but it can certainly be said those are getting-gray-in-the-tooth ages," an NFL general manager said of Brady, McNabb and Manning. "It just makes sense that all three at this stage in their careers are more susceptible to injury and I definitely see each one facing unique, pressurized situations this year.
"Peyton's defense supporting him is suspect and you can tell the Colts do not like their left tackle situation. I think Peyton has as much pride and competitive spirit as any quarterback in the league, so, that is going to serve him well through the changes. McNabb is always under great pressure in Philadelphia. They really are never going to truly appreciate him until he wins a Super Bowl or until he moves on. He looks like this year he is just going to face the music and just play. His offensive line is good on paper, but we'll see what it is on the field. And Brady has to be a little apprehensive coming off that injury. And is the knee going to hold up? His defense is suspect. I think he and that offense are going to have to outscore people."
Nearly every individual in the Patriots organization -- from owner Robert Kraft downward -- still firmly believes that Brady is the NFL's best quarterback.
Brady last week in a Patriots news conference said about his injury: "I don't think about it. I don't lose sleep over it."
Brady added about his Patriots tenure: "You take on a different role here every year based on how long you've been here."
Brady appears to understand the scrutiny, the pressure on him to return the Patriots to champions this season. The three-time champion won his last Super Bowl in 2005. Manning won his lone ring in 2007.
McNabb is hearing that in 2009 he has his best chance for his first title because the Eagles have added offensive weapons in Vick and high offensive draft choices Jeremy Maclin (receiver) and LeSean McCoy (running back) to complement big-play running back Brian Westbrook and receiver DeSean Jackson.
"You bring a guy in here who is 20 years old and ask him to be an all-pro?" McNabb said. "Well, you can ask, but we know that does not happen a lot. We all want them to come along but I think the bigger thing is for the guys who have been here longer to elevate their games. We cannot expect the young guys to lead."
McNabb said he views his experience, his longevity far from being a hindrance.
"I've been doing this a lot of years here," he said. "When you are around a place 11 years, people know how you operate. The bottom line is I'm very serious about winning."
Manning faces this season without receiver Marvin Harrison, offensive coordinator Tom Moore and coach Tony Dungy.
"We have some new receivers, so, my challenge has been getting as comfortable as I possibly can with each receiver," Manning said. "I need to get my timing down so I know exactly where they are going to be and we need to get where they're comfortable hearing my audibles and knowing the different adjustments of our offense. My goal is to get my timing with these young guys to like what I had with Marvin Harrison and like what I have with Reggie Wayne.
"I don't know if you ever really replace Marvin Harrison. I think you simply adjust to it. I think all the players are getting to know coach Caldwell and he's getting to know us. Transition and change is part of the NFL and we're going to continue to work hard."
Brady, McNabb and Manning have enough NFL wisdom to build a mindset for the unexpected this season. They already know the unique pressures of a veteran quarterback under fire. But this trio also knows something bolder is brewing for each in the 2009 season.
Call it heat sensory.