The "NFL's best running back" distinction has changed hands so frequently and is so fleeting for those who own it that declaring a back to be the best in the league at his position has almost become pointless.
That's not to say that Derrick Henry, Dalvin Cook, Christian McCaffrey, Alvin Kamara and Nick Chubb aren't all awesome players. It's just that, at this point, all it takes is a big week or two for a new back to take the throne.
It wasn't long ago when the league's running back hierarchy was unmistakably led by Ezekiel Elliott, Saquon Barkley and Todd Gurley, who ranked 1-2-3 in rushing yards in 2018. Gurley (the 2017 Offensive Player of the Year) and Elliott (the 2018 rushing champion) were All-Pros that season, and Barkley was the Offensive Rookie of the Year.
A year-and-a-half later, none of those three are part of those conversations. Elliott hasn't been effective enough, Barkley hasn't been healthy enough and Gurley is basically washed up at the age of, um, 26.
Early in 2019, McCaffrey was all the rage (the Carolina Panthers stud compiled a silly 1,576 scrimmage yards and 14 touchdowns in his first 10 games), but then Henry took over with an even sillier 896 rushing yards and 10 touchdowns during the final six weeks of the Tennessee Titans' 2019 campaign. Meanwhile, Chubb arguably had a more balanced season than both and wound up the runner-up for the rushing crown as a breakout member of the Cleveland Browns.
Now, it's McCaffrey who can't stay on the field. Henry has been fantastic but ranks outside of the top 10 in yards per rushing attempt. Chubb actually leads all qualified backs with a 6.1 mark in that metric, but he's been limited to just five games as a result of a knee injury.
It's undoubtedly Cook's turn. The Minnesota Vikings back has accumulated a comical 590 scrimmage yards and six touchdowns in his last three games to almost singlehandedly keep Minnesota alive in the playoff race. Cook is on pace to score 23 touchdowns, and his yards-per-game average of 119.3 is more than 14 yards clear of the second-place Henry.
But even before Cook grabbed the likely temporary crown from Henry, Kamara had his day in the sun. A quarter of the way through the season, the versatile New Orleans Saints back was on pace for 2,228 yards from scrimmage and 28 touchdowns. Five weeks later, he's still on track to eclipse 2,000 yards as a rusher and receiver and score 20 touchdowns, but he's become old news as a result of Cook's emergence.
Who's next? Consider Ronald Jones II of the Tampa Bay Buccaneers, who was punchline-level bad as a rookie in 2018 and only slightly more productive in 2019 but now ranks third in the 2020 rushing yardage race after a 192-yard performance in Week 10.
Since Week 4, Jones' 5.6 yards-per-attempt average trumps Henry, Cook, McCaffrey and most other qualified backs. But wait, don't rule out Philadelphia Eagles sophomore Miles Sanders, who leads all backs with a 6.9 average during that stretch.
Who will we be talking about in that "best running back" conversation at this point next year? We might already be over Cook and Henry, and Jones might have already handed the baton to Sanders or an emerging rusher such as Damien Harris of the New England Patriots (5.5 yards per carry in six games this year), D'Andre Swift of the Detroit Lions (5.0 yards per carry and 181 receiving yards in his last six outings), J.K. Dobbins of the Baltimore Ravens (5.4 yards per carry thus far in his rookie campaign) or James Robinson of the Jacksonville Jaguars (ranks behind only Cook, Kamara and Henry in scrimmage yards).
This isn't a totally new phenomenon. Gurley, Kareem Hunt, LeSean McCoy and Le'Veon Bell were the league's top four rushers in 2017. All have since bounced to new teams, and Hunt, McCoy and Bell are essentially backups.
The year before that, only Elliott had more rushing yards than Jordan Howard, DeMarco Murray and Jay Ajayi, none of whom are currently employed by NFL teams.
McCoy, Elliott, Gurley and Bell all experienced nice extended runs, but flashes in the pan (so far or almost certainly forever in some cases) such as Ajayi, Howard, Murray, Doug Martin, James Conner, David Johnson, Leonard Fournette, Alfred Morris, Chubb, Jones and Cook have taken turns in the spotlight so interchangeably that you wonder if we'll ever have another McCoy or Elliott let alone another Adrian Peterson (who truly was "the man" between 2007 and 2015).
That's just not how it works at most other positions.
This year's most prolific receivers, DeAndre Hopkins and Stefon Diggs, have a combined seven 1,000-yard seasons under their belts. Hopkins, Michael Thomas, Julio Jones, Mike Evans and a few other wideouts have been consistently dominant for much of the last decade.
Veterans such as Andrew Whitworth, David Bakhtiari, Terron Armstead, Zack Martin, Marshal Yanda (until his recent retirement) and a few others have held a death grip on the offensive line superstar market for years, and it doesn't appear as though newbies such as Ronnie Stanley, Quenton Nelson or Laremy Tunsil will be fading anytime soon.
And how long has it been since we've debated the merits of the best defensive players in the game without touching on Aaron Donald, Khalil Mack, J.J. Watt or Von Miller? New guys such as T.J. Watt, Nick Bosa and Myles Garrett are of course joining that party, but again, those reigns don't appear as though they'll be short-lived anyway.
This is all a byproduct of the obvious: The running back position has the shortest shelf life in professional football, by a wide margin. It's easy to get hurt when you're getting hit as often as these guys do, and it's easier to lose your featured role because of injury or the threat of injury. That means more platoons and more volatility, especially in the most pass-happy era in NFL history.
Still, it's wild to see in comparison to past eras when backs such as Jim Brown, O.J. Simpson, Walter Payton, Barry Sanders, Emmitt Smith, Marshall Faulk and Peterson enjoyed extended runs on a throne that no longer remains very warm.
Those days may be gone. So enjoy it while it lasts, Dalvin.
Brad Gagnon has covered the NFL for Bleacher Report since 2012. Follow him on Twitter, @Brad_Gagnon.