The story of the 2018 NFL trade deadline was the wide receiver market. In most seasons, the deadline doesn’t have a defining story, but this year a striking number of teams made upgrades to their pass-catching corps.

The reigning Super Bowl champion Eagles added Golden Tate, sending a third-round pick to Detroit for a half-season rental of the yards-after-catch star. The Texans shipped a fourth-round pick to Denver for deep-ball threat Demaryius Thomas a week after losing deep-ball threat Will Fuller V to a season-ending knee injury. On October 22, the Cowboys sent a first-round pick to the tanking Raiders for Amari Cooper. A month before that, the Patriots gave a fifth-round pick to the Browns for the occasionally used talents of Josh Gordon.

The NFL simply doesn’t have flurries of activity like this. Before 2018, there had been only four noteworthy in-season receiver trades since 2010. Four happened this year alone, and all four involved marquee players—Pro Bowlers picked in the first two rounds of the NFL draft. In each case, the wide receiver who was traded went to a team that’s within striking distance of a playoff spot.

This uptick in receiver action may be the byproduct of 2018 being the greatest offensive season in football history, by virtually any available metric. Nearly every quarterback in the league is putting up numbers that would have made him an icon 20 years ago. (Every quarterback who doesn’t play for the Bills, that is.) You can’t have too many pass-catching options these days; you can have only too few.

The Chiefs trot out Travis Kelce, Tyreek Hill, Sammy Watkins, and Kareem Hunt to go with Patrick Mahomes II, while the Rams have Todd Gurley, Brandin Cooks, Robert Woods, and Cooper Kupp to complement Jared Goff. The Eagles, Texans, Cowboys, and Patriots clearly made these moves in an effort to keep pace. But trading for a wide receiver is no sure thing.

There have been 13 in-season wide receiver trades since 2000. Here is the complete list; most have been duds. (For the purposes of this post, the only trades considered were those in which a receiver played games for two teams in the same season. However, there isn’t much history of preseason wide receiver trades being productive, either.)

In-Season Wide Receiver Trades Since 2000 Receiver New Team Season YPG After Trade TDs After Trade Receiver New Team Season YPG After Trade TDs After Trade Kelvin Benjamin Bills 2017 36.2 1 Percy Harvin Jets 2014 43.8 1 Mike Thomas Lions 2012 3.1 1 Derrick Mason Texans 2011 0.9 0 Deion Branch Patriots 2010 64.2 5 Randy Moss Vikings 2010 43.5 2 Braylon Edwards Jets 2009 45.1 4 Chansi Stuckey Browns 2009 18 1 Roy Williams Cowboys 2008 19.8 1 Chris Chambers Chargers 2007 55.5 4 Jerry Rice Seahawks 2004 32.9 3 Quincy Morgan Cowboys 2004 28.9 0 Antonio Bryant Browns 2004 54.6 4

The one indisputably successful in-season receiver trade this millennium was the Patriots’ acquisition of Deion Branch in 2010. He made an immediate impact, going for 98 yards in his first game after the swap and finishing the campaign with 706 receiving yards and five touchdowns, plus a sixth score during the playoffs. Of course, Branch had already played four seasons with the Pats before having a less-successful stint with the Seahawks; this move just reunited him with his old team. Take note, NFL front offices: The best way to ensure that an in-season wide receiver trade will be successful is to acquire a player who has already been named Super Bowl MVP playing alongside your team’s Hall of Fame–caliber head coach and quarterback.

The other trade that could be deemed a success was the Chargers’ 2007 deal for Chris Chambers, as he went from a Dolphins team that finished 1-15 to a San Diego squad that reached the AFC title game. That said, Chambers was averaging nearly 70 receiving yards per game that season with Miami, and averaged just 55 with the Chargers. The next-best move would be … uh … the Jets’ 2009 decision to trade for Braylon Edwards?

By and large, most of these trades were abject failures for the teams that landed receivers. Randy Moss’s return to the Vikings wasn’t as successful as Branch’s return to New England, as he got into a power struggle with head coach Brad Childress and was cut after just four games. Even though Percy Harvin and Jerry Rice both experienced double-digit yardage-per-game increases after they were traded, both of their careers took subsequent downturns: Harvin spent just a half-season with the Jets in 2014 before petering out with the Bills, while Rice’s stint with the Seahawks ended his career. Roy Williams managed just 198 receiving yards in 10 games for the Cowboys in 2008 after leading the league in receiving yardage in 2006; that was a massive disappointment, considering that Dallas gave up four draft picks to get him. Derrick Mason’s career ended after he was traded to the Texans. Kelvin Benjamin … well, it’s not looking good with the Bills.

I don’t think people fully understand how difficult it is to play receiver. NFL receivers are among the best athletes on the planet, so fans can sometimes think that the position requires little more than pure athleticism. This is why some argue that fast college quarterbacks should move to wide receiver upon entering the pros. But playing receiver is incredibly hard. Most college quarterbacks who transition to receiver fail, and time and again we see that the position is not as simple as lining up and going deep. Of the 13 receivers taken in the first round of the 2015-17 drafts, only two managed to rack up more than 500 receiving yards as rookies.

Teams ask receivers to react to defenses in different ways. And so much of being a good receiver involves establishing a rapport with a quarterback: understanding not only how to get open, but how to get open exactly where the QB expects. These are mental asks, not physical ones. It might require weeks or months for a receiver to jell with his quarterback, which is why it’s helpful for receivers to be in a given offensive system in OTAs or preseason training camp. Even then, a strong rapport may never form.

This is why in-season receiver trades are so rare. Sure, some of the lack of success from recent deals comes from circumstance. In many scenarios, the players were washed when they were dealt. In others, they were traded to teams who put them in less favorable situations.

It’s possible for Tate, Thomas, Cooper, and Gordon to find success with their new teams. But with wide receivers, the formula is never as simple as plug-and-play. Maybe these four players will establish the elusive link with their new QBs. History doesn’t mean much when it comes to NFL offenses anymore, but it’d suggest that in all four cases, it may already be too late.