I think a lot of them probably know that their time is short in whatever sport they are playing, so they just kind of roll with the punches as much as they can knowing it won't last forever. Unless they are an all star or some kind of franchise player, things aren't set in stone at all. My wife's cousin played for the NFL. I think he was only in the league maybe five years before the injuries forced him to quit. I think that is pretty common in terms of a career lifespan.
The risk of injury must always weigh on the back of the mind, right? Falling wrong, a bad tackle, a slip at practice - can all be career enders.
The Lions? :)
Nope, Broncos and Patriots.