Paris Saint-Germain manager Unai Emery's baffling decision to select a team devoid of an organising midfield player against Montpellier on Saturday proved a costly oversight.
PSG were embarrassed, battered 3-0 by a side that had won just once in their last six games.
Emery's inexplicable lineup meant his team squandered a chance to move temporarily top and may have fatally undermined his relationship with key playmaker Hatem Ben Arfa.
The switch back to 4-3-3 after the 4-2-3-1 formation had appeared to finally be getting positive performances out of his players is hard to explain. So too is the decision to leave Ben Arfa on the bench despite injuries to Thiago Motta, Adrien Rabiot, Marco Verratti and Javier Pastore.
Ben Arfa is as gifted as any of his team-mates at the Parc des Princes and can change a game with a moment of individual brilliance. Last season, with OGC Nice, he scored 18 goals and assisted seven more for his team-mates.
He was one of only three non-PSG players to be named in the Ligue 1 team of the year.
His individualism was encouraged, and Les Aiglons were rewarded as they finished fourth. Not since the 1975-76 season have Nice finished higher.
His delicate mentality is well known and has been the deciding factor in his failure to reach a top club before now.
If he is to perform at his best, he must be handled with care. This may be less than ideal for a professional footballer, but it is an established reality.
The football world was certainly fully aware of Ben Arfa's predilection for special treatment before he was offered a contract by the French champions. His dismal displays in English football, contrasted occasionally with displays of breathtaking brilliance, were symptomatic of it.
Emery's reluctance to use Ben Arfa has been evident throughout this season, but against Montpellier, it was an inexcusable decision.
Rolland Courbis, the former manager of Montpellier and nine other Ligue 1 clubs, was highly critical of Emery's decision to leave the 29-year-old on the sidelines until the match was lost.
Commenting on RMC (via Foot01.com), Courbis pointed out the fact that Ben Arfa was left out despite the absences of Verratti, Pastore, Motta and Rabiot. "In his place, I would not know what to think."
Emery's difficult relationship with Ben Arfa is hardly a revelation.
After a training-ground argument, the Spaniard reportedly told Ben Arfa that he is "no Messi," adding "you can't win a game on your own," according to Le Equipe (via AS).
Struggling for opportunities to show his undoubted ability, Ben Arfa was idiomatically said to be "eating his black bread," per AFP (via Eurosport).
In recent weeks, though, the former Newcastle United man has emerged as one of PSG's most influential players. His introduction from the bench against Arsenal sparked a comeback that culminated in a hugely significant 2-2 draw.
He was something close to his untouchable best against Angers too, yet he was reduced to a helpless spectator as his team-mates were thrashed by Montpellier.
The speed of movement and speed of thought that he brings to Les Parisiens' attack is unmatched by his team-mates, and while he may not be Lionel Messi, he can win games single-handedly.
He has greater vision than Lucas Moura, beats his man more easily than Verratti and possesses a more dangerous shot than Angel Di Maria.
His flexibility means he is able play anywhere across the attacking line.
Against Montpellier, Di Maria was forced to vainly drop from his wide position in an attempt to orchestrate the play. Paris were utterly uninspired and incapable of thoughtfully constructing attacks. The hosts were able to surround and dispossess PSG's attackers as they fruitlessly searched for a passing outlet.
The pace and clever movement of the front three of Di Maria, Edinson Cavani and Lucas can do little when the ball only reaches them in isolated positions far from goal.
Ben Arfa's eventual introduction, with Paris 2-0 down, coincided with a significant improvement. He immediately penetrated what had been an otherwise largely untroubled Montpellier back line and played in Lucas for what could so easily have been a goal and PSG's route back into the game.
In the post-Zlatan Ibrahimovic era, Paris Saint-Germain do not possess a transcendent player and cannot afford to leave a player of Ben Arfa's ability out of the team without cause.
Emery cannot simply send out a trio of holding midfielders and expect his forward line to win him the game.
Aware of Ibrahimovic's absence, and emboldened by it, other Ligue 1 clubs see Paris is a vulnerable foe.
After the capitulation, Emery rather lamely suggested to the press that Ben Arfa was not fit enough to start against Montpellier.
His energetic cameo suggests that he at least had the energy to start the match, even if he could not have completed it. Given that Ben Arfa has played a full 90 minutes just twice this season and has been used as an impact substitute 10 times, it seems clear Emery is unwilling to trust the enigmatic playmaker.
Fitness concerns seem little more than a convenient smokescreen.
That is the key concern, and with Verratti and Motta likely to return for the looming Champions League match against Ludogorets Razgrad, Ben Arfa will likely remain on the sidelines. If that is the case, it will be to the detriment of PSG's domestic and European ambitions.
That move would cost the capital club in excess of £30 million, but the fact Ben Arfa arrived on a free transfer in the summer means there is little financial concern about simply deeming him a failed experiment.
Were PSG to invest such a significant fee in a player with a largely similar skill set and natural position to Ben Arfa, it would suggest that the club's hierarchy is ready to do just that.
With the Ludogorets and Nice games on the immediate horizon, Emery has two opportunities to resolve his issues with the attacking midfielder and put him to good use.
If Emery leaves him out and Paris suffer further humiliation, it could be the boss and not Ben Arfa who leaves Paris first.