Just when there was a bit of momentum at Manchester United, and doubts about Ruben Amorim's much-maligned formation were vanishing - then came the loss to Everton.
It was a game that put the Amorim project back to square one in terms of how much faith there is in this specific era. Gary Neville said the complacency shown by United will erode confidence in the team - but there was just as much criticism about the 3-4-2-1 system.
Despite playing over 75 minutes with an extra player after Everton's Idrissa Gueye was sent off, Amorim chose to stick with his preferred formation - keeping three centre-backs and two wing-backs on the pitch.
"You have five at the back, why?" asked Neville, while Jamie Carragher added: "I don't understand how you can stick with something so steadfastly in a situation like that. You don't need three [centre-backs] there."
Next up for United is a trip to Crystal Palace, where Oliver Glasner has made a success of that 3-4-2-1 formation. The Eagles sit in the top five - where United want to be - having won a trophy via the FA Cup, which has eluded Amorim in his year in charge thus far.
Glasner's formation has even survived the departures of Michael Olise and Eberechi Eze, highlighting how the system thrives on more than a few top-level players - it is a collective structure that works. How United need that at the moment.
"We have found a system where we are very balanced, where we can threaten the opposition goal and also be very consistent in our defence," said Glasner last month. "That's why we stick to it."
So why does it bring success for Palace, but less so for Man Utd? Using the Palace boss' own words, we take a look at Glasner's formation from back to front.
The back three
The back three of Chris Richards, Maxence Lacroix and Marc Guehi have marshalled things brilliantly in front of Dean Henderson - one of the statistically best goalkeepers in the division.
Palace have the Premier League's second-best defence in terms of goals conceded - and are one of only two backlines to let in a single-digit goal tally after a dozen Premier League games. The other team is league leaders Arsenal.
The central areas are the most important part of the pitch for Glasner, as it is the most vulnerable area for any side. "The centre determines the game. It starts with the back three - you're talking about the core," he says.
One of the reasons three centre-backs is a good system in the modern Premier League era is the way wide centre-backs protect the 'half space'.
It is the area where most dangerous attacks emerge from via defence-breaking passes or runs - these areas are also described as the 'pockets'.
As Glasner says: "The half runs, which is where most of the assists are coming from, in defence you have to protect these areas." And Palace appear to have the right profiles in those centre-back positions.
No Premier League defender has more interceptions this season than both Richards and Lacroix, while only six defenders have won more possession in the defensive third this season than Palace captain Guehi.
Even Neville spoke about the importance of positioning the three centre-backs on Monday night against Everton. "Matthijs de Ligt is much more dominant and certain in that central role," he said. "When Harry Maguire plays, De Ligt goes into the right channel where he gets caught out and doesn't look comfortable."
Palace have perfected their back three, but on the basis of recent displays, United need a bit more work.
The midfield four
The four in Palace's midfield are divided into two areas: the wing-backs and the two sitting midfielders.
The flying wing-backs of Daniel Munoz and Tyrick Mitchell are critical to this Palace team because of the intensity they bring.
Munoz is the most intense player in the Premier League, clocking nearly 14.5km per game at high intensity this season - nearly 1.5km more than the next-best player.
It is not a singular thing to Munoz, it is part of Glasner's instructions. That's because Mitchell, on the opposite flank, sits fifth for current Premier League players in the same metric. Palace are the only team in the Premier League with two players in the top dozen top-flight players in this category.
What is more striking is how Palace's wing-backs compare to Man Utd's wing-backs. For example, Munoz runs further per game at high intensity than Amad Diallo and Noussair Mazrouai combined.
Meanwhile, Mitchell is streets clear of what United's left-wing-back options, Patrick Dorgu and Diogo Dalot, produce.
Then comes the importance of the two sitting midfielders - rotated between Adam Wharton, Daichi Kamada and Jefferson Lerma - who set the tone for Palace's play.
"The central midfielders, we call them the quarter-backs," says Glasner. "They are responsible for the speed of our attacks, if we go forward or keep possession. So they are important."
Palace and United's midfield set-up is similar. In Wharton, the Eagles have their own version of Bruno Fernandes - a player who sits and tries to break the opposition's lines.
"That's why the manager wants me there," said Man Utd captain Fernandes on Monday night. "To have more of the ball and control the tempo of the team.
"He [Amorim] knows I can run a lot, press high and get my body back there when we need to get to the box and defend."
Meanwhile, the other sitting midfielder - Kamada for Palace or Casemiro at Man Utd - sits and shares defensive duties with the other player.
For Palace, the system works defensively as well as offensively. Kamada sits in the top five midfielders this season for tackles won per 90, with a slightly better record than Chelsea's Moises Caicedo.
But for United, how Casemiro and Fernandes cope in midfield as a two has been much-maligned. They were cut wide open at times against Everton on Monday, with Gueye showing signs of frailty within the opening minutes.
But even after the Everton midfielder's red card, the Toffees still had joy playing around United's midfield two - with the winning goal coming from direct passing through the middle of the pitch.
The No 10s behind Mateta
But it is not just Palace's sitting midfielders who play Glasner's side progress the ball centrally - the two No 10s also help to create overloads in the most important area of the pitch.
"We try to play with the two No 10s narrow, with the striker - so we can maybe have eight players in the centre to combine together," says Glasner. Those eight players being three centre-backs, two sitting midfielders, two attacking midfielders and one striker.
"You can't pass with one touch if players are 30 or 40 yards away from each other in the distances," Glasner added. "You need connections on the pitch."
The two No 10s, normally Ismaila Sarr and Yeremy Pino in this Palace team, are helping them to break through the middle of the pitch by creating a four-man box with the sitting midfielders. No matter if you face a team with two or three in midfield, you will always have an overload.
But they also assist in pinning opposition teams back. "Some teams mark our No 10s with their No 6s [defensive midfielders] - so they're pretty much playing with a back six," says Glasner.
If a busy striker like Jean-Philippe Mateta can occupy multiple centre-backs at once - as he tends to do - then the two No 10s need to be marked by midfielders. If they aren't, the likes of Sarr and Pino have more space.
All those eight players being central can create a very congested area in the middle of the park, but Glasner has plans for that. "If the opposition closes the middle, then somebody can drop out and you can overload the wing," he says.
Palace's front three is a perfect system set up by the right profiles. "You need pocket players, you need runners - the mix makes it," he says. The pocket players are Sarr and Pino, the runners are Munoz and Mitchell.
It allows Mateta to do what he does best - be physical and hold the ball up. Mateta ranks top for the number of hold-ups in the Premier League this season.
"You need the right players for it," says Glasner about his attack. "You can't ask all the players making runs in behind if they are used to playing in the pockets."
United tried to address these forward areas in the transfer window, forking out big fees for Benjamin Sesko, Bryan Mbeumo and Matheus Cunha.
They fit the United structure in places, as has been seen this season in bright attacking moments. But any injuries - such as Cunha and Sesko's this past week - and there are holes. And they are holes that Palace do not seem to have.