Every once in a while, that once promising career comes to an abrupt end. Or that one-time legend fizzles out due to the wear and tear of the game.
Career-ending injuries, a player getting into legal trouble or just an early retirement all result in the question no one ever wants to hear, "what if?"
For these 17 players, by whatever means, NFL careers came to a melancholy ending.
As soon as Lawrence Taylor hit Joe Theismann, he knew something was wrong.
As you can see, the leg break was enough to end Theismann's career at the age of 36.
Theismann is in the Washington Redskins Ring of Fame.
Throughout his career, Randy Moss has been a troublemaker.
No one could really figure out how to calm him down, and many questioned whether the 1,000 receiving-yard seasons were worth the trouble. Moss' production fizzled in 2010 with a lack of concentration.
After apparently spending much of the offseason at his West Virginia home getting into great shape, Moss refused offers from several teams, claiming that the money wasn't right.
Will anyone ever figure Randy Moss out?
You may remember this one, as it occured quite recently.
Everett suffered a life-threatening spine injury, and doctors believed that he may not ever walk again.
However, Everett was seen walking a few years ago under his own power.
Props to the Buffalo Bills for keeping him active long enough to qualify for full pension.
Gale Sayers retired at the age of 29 due to multiple knee injuries.
Before those injuries, Sayers was a lightning-fast back who recorded 22 touchdowns in his rookie season.
The knee injuries took their toll, and Sayers lost his burst. He was still inducted into the Pro Football Hall of Fame.
Barry Sanders is, depending on who you ask, the greatest RB of all time.
Had he continued his career instead of retiring at the age of 31, Sanders would hold the records to prove it.
The former Detroit Lion was one of the quickest and most agile players to ever play the game.
Favre's story is well known.
One of Favre's best opportunities to retire was in 2007 after the Packers had been defeated by the New York Giants in the NFC Championship Game.. However, he didn't stay retired long.
After an unsuccessful stint with the Jets, he had an opportunity to retire after the best statistical season of his career with the Vikings, and the Jenn Sterger scandal and injuries are history.
Though Irvin suffered a neck injury, it was not as severe as some of the others on this list.
What looks like a fairly commonplace tackle ended Irvin's career, although he did enjoy a lengthy career before it ended.
To make things worse, Eagles fans inexcusably cheered the injury.
Another promising career comes to an abrupt end.
Dennis Byrd's stock was a great pass-rusher, as he had recorded 27 sacks in his first three seasons as a defensive lineman for the Jets.
However, a brutal neck injury changed all of that.
The Dennis Byrd Award for the Jets' most inspirational player was named after him.
Derrick Thomas was drafted with the fourth overall pick in the 1989 draft, whose first five picks featured Troy Aikman, Tony Mandarich, Barry Sanders, Thomas and Deion Sanders.
Thomas was one of the greatest pass-rushers of all time.
Unfortunately, Thomas' career was cut short after a tragic car accident that resulted in his premature death at the age of 33.
Utley's famous thumbs up sign as he was carted off the field in the Detroit Lions has become a symbol for him.
Injuries plagued his career before the start of his third season, but just as it looked like he might be healthy, he suffered a neck injury.
A former third-round pick, the tragic accident ended his career.
Jack "The Assassin" Tatum, had delivered many big hits in his career.
It just happened that this shoulder-to-helmet blow ended Darryl Stingley's career. For the clarification, the famous hit was legal.
Stingley never fully recovered from the hit, as most football-related neck injuries have serious life-long implications.
Stingley died in 2007 of heart disease complicated by quadriplegia.
If you don't believe Barry Sanders is the greatest RB in NFL History, chances are you might believe that Jim Brown is.
However, these two running backs have one thing in common. Their careers ended early.
Brown's punishing style of running took a huge toll on his body, and after nine years, he made the decision to retire.
The former sixth-overall pick may be glad he retired, as he is healthy today at the age of 75.
Like Kevin Everett's story, this one happened recently. However, the result is much worse than what happened to Everett.
Ever since being drafted, Henry had been involved in legal trouble. He hadn't played a full season in his career mainly due to suspensions.
However, in 2008, Henry attempted to get his life back on track and stayed out of legal trouble.
After falling off his fiancee's truck, Henry died due to trauma to the head. His organs were donated and helped save four lives.
It was a tragic accident to a young man trying to get his life headed in the right direction.
Eric Dickerson was a stellar running back. He was among the biggest and most successful running backs during his tenure with the Rams.
Dickerson was traded to the Colts after contract disputes with the Rams, but he still enjoyed time as an elite running back.
After being traded from the Colts to the Raiders to the Falcons, Dickerson was again traded to the Packers where his career ended after a failed physical.
A former first-round draft pick, Sharpe's career was cut short after seven years.
Looking back on his career, many speculate as to whether Sharpe could've broken some of Jerry Rice's records.
However, a neck injury ended what could have been one of the greatest careers of all time.
A hit from Aeneas Williams ended Steve Young's career. But it wasn't just Williams' hit that helped end his career.
Young had suffered many concussions during his football career and was unable to continue playing due to them.
Though the 49ers' star QB was 37 years old, he was still a productive QB and had a few years left in the tank.
The NFL has tried to eliminate injuries to the head, as Young is an example of what they can do to a career.
Drafted with the fifth overall pick in the 2004 NFL draft, big things were expected of Taylor.
Taylor was a hard-hitting safety that seemingly was everywhere. But like Chris Henry, he had off-the-field problems.
Taylor, like Henry, tried to turn his life around, citing his daughter as a primary reason.
At the age of 24, Taylor was shot and wounded in his Miami home, injuries of which he would die from.
No one has worn No. 21 on the Redskins since, and it's a sad ending to someone who was trying to get on the right track for the ones he loved.
Hopefully for the both of these players, these neck injuries aren't the end of their careers.
Manning has had several surgeries on his neck, something that has bothered him before.
Collins suffered a season-ending and career-threatening neck injury earlier this season. In six months, doctor's will re-evaluate the 28-year-old Green Bay safety to see if he can play again.
The two players both had similar surgeries done to them recently.
Both of these players likely won't see the field until next year, and hopefully, they will both be able to continue their careers come next season.