The end of Tony Romo's career -- and make no mistake, it is the end -- serves up a vivid reminder of a hard, cold truth about professional sports: Greatness remains a truly elusive thing.

Tony Romo is 36 years old. His latest injury seems like a further curse against one of this generation's greatest quarterbacks who will accomplish nothing, not really, not in the context of his otherwise stellar career. It is simply, and unfairly, another illustration of his wasted time in the league. Forget this season. Forget next season. Romo has been ailed with bad luck, missed extra-point holds, injuries -- snakebit in a sport where even a little venom is enough to undermine an uber-talent's possibilities.

You doubt his greatness? You see the long line of what-could-have-beens as proof of some sort to weakness? Friendly reminder: Romo is third all-time in quarterback rating, ahead of Steve Young, Peyton Manning, Tom Brady, Joe Montana and just about every other man who has ever helmed an NFL team's offense. He is 16th all-time in game-wining drives, just a few never-will-happen 2016 come-from-behind Romo specials from passing the likes of Montana, Eli Manning and Fran Tarkenton. His passing-touchdown percentage is the same as Peyton Manning's. He's the real deal.

Tony Romo could -- the key word being could -- have been one of the game's all-time greats. But luck, talent, greatness and accomplishment hinge as much on your own talent and will as the forces out there in the world trying to prove their own value and, yes, cold-hard luck.

It is worth noting how difficult greatness truly is to wrestle from the games our most gifted athletes play. LeBron James is an all-timer, but a Spurs bounce or a Ray Allen 3-pointer here, or a Warriors shot or two there, and we would see and remember him differently. Tom Brady is the greatest quarterback of all time, but a Tuck Rule here, or a dropped pass there, and he's another great regular season NFL player. On the list goes, from Phil Mickelson to Aaron Rodgers to Steph Curry: But for one or two magical runs -- shaped by so many forces, including moments of luck or good fortune -- the world would see them utterly differently.

The Tony Romo era in Dallas looks finished. USATSI

It is a small thing, the thin margin between exquisite accomplishment and a player with a very, very good career. We focus and talk often about those who fall on the better side of this divide. But to outlast and outplay in historical terms the many other immensely talented competitors out there you must enjoy not just your own success but the shortcomings of others.

Like those of Romo.

This was the season. The offensive line, the sense the Cowboys would put so much possibility together, Dez Bryant waiting to be his own personal Michael Irvin, the vulnerability of the NFC East ... it seemed the regression to the mean would mean Romo with some postseason success to flaunt to all those rapid haters.

That's over now. A 36-year-old quarterback with a history of back issues cannot and should not be counted on when he breaks a bone in his back. In a random preseason play. The end is nigh. The Romo era has drawn to a close.

It is a real, true shame. Romo has played 12 seasons in the NFL, and yet he has been able to make the playoffs just four times. He has won two -- two -- postseason games. That's simply atrocious.

Yet Romo's touchdown-to-interception ratio in the regular season is roughly 2-to-1, yet in the postseason it improves to 4-to-1. Most great players who excel as clearly as Romo has eventually break through. Maybe not in a championship -- although, often, that is the case -- but at least with a level of playoff respectability that reflects their skill, their career and an approximation of what should be their legacy.

That will not be true for Romo. He will not break through. He will not win the validating Super Bowl that so many greats have achieved at the end of their otherwise wonderful but until-then incomplete careers. He will not have his moment of validation.

Dak Prescott? He could be -- even might be -- a young man about to embark on a tantalizingly promising career. But it is Romo who reminds us that promise, even greatness, do not necessarily translate into true and memorable accomplishment.