How fast is the NFL? Whats the speed of their learning? How quickly do they adapt to a new beast?
Conversely, how long can someone really rise above their peers at such an elite level?
I think the answer to all of those questions lies in the Patriots 2007-2008 season. Their season was the most interesting -and informative- season I've ever seen. They started out very strong and were routinely beating opponents by three or four touchdowns. Their dominance extended through nine games. It culminated in a 56-10 drubbing of the Buffalo Bills.
Interestingly, the Patriots were booed by the fans. They were "too good".
Just one game later they barely won by three points against an inferior Ravens team. Then they began an impressive winning streak until the Super Bowl, where they lost by three points. However, the second half of the season was highlighted by close calls, narrow victories, and Tom Brady's out-of-this-world play which kept them ahead of the curve.
However, the season shows that no system of players and coaches, plays and training, can peak for longer than about 11 weeks.
In World War I combat doctors realized that after 200 days of intense combat men became so melancholy from "battle fatigue" that they were no longer effective fighters. I am definitely not comparing World War I to football, but there is a common theme that humans can only endure so much sustained, superior effort before they either fall back or are caught from behind. There is only so much willpower stored in the human soul.