There are numerous reasons why the Philadelphia Eagles collapsed this year. The team started 10-1 and that was followed by losing six of their last seven games. But there's one reason that's the biggest by far. To look at that, we need to go back to this past summer when everyone, and I mean almost everyone, thought the team had the best roster in the sport.

I did. You did. Your cousin did. And not just Eagles fans believed this. Many in the league did. And many who cover the league. In August, ESPN ranked Philadelphia's roster as the best in the NFL. It was a smart take. The team had one of the best pass throwers in the league in Jalen Hurts, one of the top receiving groups, and what is generally seen as the best offensive line. It all made sense.

Pro Football Focus also ranked the Eagles' roster as the best in the league, writing in early September: "The Eagles have the best quarterback in the NFC. They have dynamic weapons on offense. Nobody in the league is better in the trenches. There are sore spots in the middle of their defense, but they have as good a chance as anybody to get back to the Super Bowl."

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"The Eagles front office seems to hit on a rate higher than maybe even Jalen Hurts’ completion percentage," wrote Deadspin.com in November. The site added that Howie Roseman, the team's executive vice president and general manager, made things easier for the team since Roseman and his staff are "excellent at their jobs (allowing) the players to do the heavy lifting of playing NFL football with the confidence that the man beside him is a competent professional."

This isn't to pick on any individual site because, again, we all did it. I definitely believed it.

There's just one problem: It may not have been true.

The problems with the Eagles are many. Hurts, as analyst and former Super Bowl winner Troy Aikman noted, may be more injured than he's letting on. Coach Nick Sirianni also went full Ray Handley and was totally and completely clueless on how to fix the problems of the team. There were other injuries. Lots of things went wrong.

But that doesn't explain everything. A collapse like this is far more structural. It's likely, if not completely true, the problem is the Eagles' roster isn't nearly as good as we all thought it was.

Tampa Bay's receivers ran through the Eagles' secondary, sometimes barely touched. NFL.com says the Buccaneers finished with 219 yards after the catch and the large number of missed tackles isn't just coaching or practice habits. That's a personnel problem.

There's little chance that you'd look at that Eagles' roster now and rank it as the best in football.

This isn't recency bias. We have a nice body of work to judge from. There's really no other conclusion.

So wait a second? Was the roster terrible when they were kicking everyone's butt? When they made the Super Bowl just a year ago? You're not making any sense, Mike. Stick to writing about Star Trek, you loser.

The true test of a great roster is how it holds up over a season or, actually, several seasons. When attrition hits. When injuries hit. When the season becomes brutal and a team gets punched in the mouth. That's the true test of a great roster.

The Baltimore Ravens are a good example of this. They lost one of the best tight ends in football in Mark Andrews, some other pieces, and they just churn along. That roster is so talented and deep if you broke it into pieces it could potentially spawn two playoff teams.

That's what we all thought the Eagles were.

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In June, ESPN did something else that in retrospect was pretty incredible. The site ranked every team's core, defining core as not how many sit-ups Terrell Owens can do but instead "the five most important players to a team...the guys each roster is built around." The Eagles' core was ranked third:

"Roster core: QB Jalen Hurts, WR A.J. Brown, OT Lane Johnson, OLB Haason Reddick, CB Darius Slay. Average core age: 28.8. The Eagles’ elite core checks every positional value box, with high-end players at quarterback, wide receiver, offensive tackle, edge rusher and corner. And in reality, this exercise undersells the strength of the Eagles as a whole, because there are very talented players left off the list, including cornerback James Bradberry, receiver DeVonta Smith and center Jason Kelce. But even just looking at the five above, it’s easy to see why the Eagles are favorites to win the NFC again."

That is a great core. Most likely. Probably.

We think. Right?

Right?

This article originally appeared on USA TODAY: What happened to Eagles this season? How promising team collapsed