Title windows for NE, DEN, PIT

Tom Brady and Bill Belichick have made the Pats contenders, but they won't be there forever. AP Photo/Elise Amendola

Sustained success in the NFL, especially when compared to its major North American professional sports counterparts (NBA, NHL and MLB), is arduous to achieve.

The Atlanta Falcons slid from the top seed in the NFC in 2012 to the basement of the NFC South in 2013. The Washington Redskins went from being a middling squad to the playoffs in 2012, only to regress back to the bottom of the NFC East last season.

Windows don't close gently in the NFL. They often collapse.

In evaluating teams whose window could soon shut, we need to establish whose is currently open. For that, we turned to the top of our Future Power Rankings list, which will be unveiled Thursday on ESPN Insider.

There are many contributing factors to a team dropping in the standings from one season to the next: crippling injuries and difficult schedules (especially following a year with a favorable schedule) are among them. But for the purpose of this exercise, we're not going to predict or project injuries. They're unpredictable. (Case in point: A healthy Andrew Luck keeps the Colts among the Super Bowl contenders for the next 10-12 years. A major injury to Luck sends them spiraling toward a 6-10 season based on the talent around him.)

The bottom line for teams whose windows close after sustained success is that it almost always derives from two factors: a change (injury, free agency departure, etc.) in quarterback, or the exposure of mediocre talent surrounding a franchise quarterback. With that in mind, let's dig deeper on three candidates whose window could close in the next three years.

New England Patriots

The skinny: Injuries terrorized the Patriots in 2013. Tight end Rob Gronkowski, linebacker Jerod Mayo, nose tackle Vince Wilfork, right tackle Sebastian Vollmer and linebacker Brandon Spikes all finished the season on injured reserve. That's not even an all-encompassing list. And yet, the prevailing narrative as the Patriots marched on to their third straight AFC Championship Game was that with head coach Bill Belichick and quarterback Tom Brady, they're always in the hunt.