Mangini leaves with a 23-25 overall record and two winning seasons in his three years as coach. But after leading his team to an 8-3 start, a 1-4 finish against the likes of Denver, San Francisco, Buffalo, Seattle, and Miami was unacceptable, and someone had to be axed.
And, as usually is the case in professional sports, the head coach is the easiest position to fix.
Did Mangini deserve to be fired? Maybe, maybe not. The offensive and defensive play calls have been very suspect at times, and the buck stops with the head coach. Many fans want both coordinators Brian Schottenheimer and Bob Sutton gone. That is an indictment of Mangini.
But he got fired because of the last five games.
And if you want to pinpoint one single reason for the collapse, look no further than No. 4.
Brett Favre was a farce down the stretch. In the last five games, he threw nine interceptions to just two touchdowns. He did not have a quarterback rating above 62 in any of those games, and for the entire season, he led the NFL in interceptions.
The arm strength was there, but the accuracy was not. The intermediate-to-long routes were non-existent for the season as Favre constantly missed his targets.
Even though the season was already over, his final performance of 20-for-40 for 233 yards, one touchdown, and three interceptions still was not indicative of how poorly he played.
And seeing the quarterback of the past outplaying the quarterback of the present was just a slap in the face. Pennington didn't play that well, but he played well enough to win, something Favre has not done lately.
The other performance-based reason for the Jets' downfall was the decline of Kris Jenkins. For 11 games, he was the best nose tackle in the NFL, including Albert Haynesworth. For the last five, the Jets might as well have had DeWayne Robertson out there manning the nose.
As a result, the once stout Jets' run defense faltered against the likes of Peyton Hillis and Maurice Morris.
Was their slumping play Eric Mangini's fault? No.
But the Jets need Jenkins, and Woody Johnson and Mike Tannenbaum chose Favre over Mangini.
The Patriots and Dolphins both finished with better records with more talent. But the main difference between those two teams and the Jets is that Matt Cassel and Pennington outplayed Favre.
Pennington won more games with a 1-15 Dolphins team than he did in any of his seasons with New York, and Cassel hadn't started a game since high school, but he threw for more yards than Favre with half of the interceptions
Was the coaching a factor? Of course it was. Clearly, Tony Sparano and Bill Bellichick outcoached Mangini. And as a fan, I'm glad he is gone because I wanted to see blood for the deplorable finish.
But until the Jets fix the quarterback, they are not getting to the root of the problem. Judging by Woody Johnson at the press conference, the front office really wants Favre to come back with a full offseason with the team
A full offseason of preparation and immersing himself further in the offense would have likely lead to a better season from No. 4.
His shoulder was also a constant source of speculation, and if an MRI Monday reveals something, then there is a tailor-made excuse for his struggles. He was also victimized at times by drops from several of his receivers, particularly rookie tight end Dustin Keller.
But when Pennington is succeeding with Ted Ginn Jr., Davone Bess, and Anthony Fasano as his leading pass-catchers, that excuse evaporates.
Now we enter the offseason, and Favre's will-he, won't-he retire charade begins. He is on record saying he will make the decision more quickly this offseason, but actions are much stronger than words.
And if Favre struggles the way he did this year, the Jets will fall short again next season, and the blame will shift to Tannenbaum.
Because if the Jets allow Favre to hamstring this talented football team again, there is no more head coach to fire.