Jürgen Klopp had to face the music on Saturday. And boy, did he not like it. “They are celebrating an non-relegation party in the changing room next door,” the Dortmund manager noted grumpily at the Weserstadion, “I wouldn’t write us off yet”. Werder’s sporting director Thomas Eichin, one of those neighbourly revellers, later clarified that the home side had simply cheered “a win over Dortmund”, knowing full well that “nothing” was won in regards to staving off the drop. The northerners are 16th going into the Christmas break on 17 points, two better off than Dortmund. Only one goal separates them from bottom-of-the-table Freiburg.

Werder’s jubilations – and Eichin’s explanation – showed that last year’s runners-up are still considered a tough opponent, one of the league’s genuine big scalps. But that reputation is waning. The 2-1 defeat on Saturday was the 10th loss of the current campaign. Enough to make everyone concerned look like “total idiots,” as Klopp conceded with brutal honesty afterwards. “We have played the worst half of the season imaginable,” added captain Mats Hummels, who was heavily involved in all three goals of the afternoon but unfortunately only credited for one. “The worries have been there for weeks. The way we have been playing, we deserve to be down there”.

There was a logic in this game’s particular outcome, at least. Dortmund were poor throughout, low on confidence and cutting edge, well below par in terms of individual performances. But in most matches, they haven’t played nearly as badly as they did in Bremen. The unprecedented slump from double winners and Champions League finalists to Bundesliga basement dwellers in the space of 30 months remains a mystery.

Media debates have homed in on the most readily-available numbers: the poor goal-scoring return despite creating a wealth of chances, and a series of defensive black-outs by seasoned pros at the other side of the pitch. But blaming the for and against columns as the causes for the malaise is a bit like blaming a fever on a patient’s high temperature. Those numbers are only the symptoms of a much more complex condition.

Klopp’s main attempt to explain the riddle has focussed on the lack of a proper pre-season due to the World Cup and many injuries in the squad. Once the batteries were “full again” in the new year, he promised, “it will be much more difficult to beat us.” In other words, there’s nothing wrong with the footballing idea as such, only with its insufficient implementation.

It’s a typical response from a dogmatic manager. Before the away game at Paderborn, he scalded a local reporter for suggesting that other teams might have “found out” his side and developed strategies for countering Borussia’s high-pressing style. “I’m not looking for a fight, so I will even answer the stupid questions,” he shot back acidly, before going on to claim that Dortmund’s plight was all down to their own failings. “If you say we’ve been ‘found out’, what does that say about the work of opposition coaches for the last few years?”, he added. “Were they unable to see what our game is?”

It’s a salient point. Done correctly, with pace and precision, Dortmund’s game can overpower the best of teams, as Real Madrid and Bayern can testify from recent experiences. But their troubles to play with the required intensity and to do the right things in both penalty boxes aside, Klopp’s side could also be the victims of their own success. Bayern haven’t been the only team to copy at least part of the Dortmund blueprint and blunt the original’s innovative effect in the process. Synchronised pressure against the ball and rapid transition has become the new orthodoxy in the league, the playing style almost everybody aspires to; from the superb Augsburg (sixth!) to the remarkably resilient new boys Paderborn (10th), Dortmund’s competitive tactical advantage has been partially eroded.

That’s not a new phenomenon, either. In 2011-12, they won the league with a (then) new points record of 81. Six of those points came from two wins over Bayern. The next year, they finished considerably worse, with a total of 66 points that included two draws against Bayern. At the time, Dortmund still had Robert Lewandowski and Mario Götze in their ranks, too. Last season, they picked up 71 points, with one win and one defeat against Pep Guardiola’s side. Take out the results against the Bundesliga’s southern overlords and you’ll get an average points return against the 16 others in the league that has markedly decreased from 2.34 (2011-12) to 2 (2012-13) and 2.1 (2013-14).

As early as that 2012-13 season, some observers wondered whether Klopp’s all-or-nothing approach needed to be modified. Dortmund haven’t been able to do that. They remain hell-bent on full-throttle-football. Ilkay Gundogan, the one man who can most effectively vary the side’s tempo , is only slowly coming back to full fitness, and he has been lacking like-minded team-mates.

Dortmund’s game is all about verticality and quick shots on goal. Prising deep teams open is, not surprisingly, very difficult for them. A ‘plan b’ is easy for journalists to suggest but Dortmund-based Freddie Röckenhaus, of Süddeutsche Zeitung, is surely right to question whether Klopp has neglected to develop different, more mature facets to their game. “It could be that they have failed to add a bit of coolness to the underdog style of the boom years,” he wrote. “Dortmund don’t seem to be able to cut open teams with a surgical knife, unlike other top teams. At times, one feels that BVB are caught up in eternal adolescence and power-sapping exuberance, and that a more grown-up football style is not even wanted”.

It’s worth remembering at this point that Klopp had vowed to employ even more aggressive tactics before the start of the season. He’d promised to create a “pressing machine”. To that extent, Dortmund have played a lot of 4-4-2 this season. It’s been football without a safety net, reliant on the individual class of his defenders to cope in situations with numerical parity or worse. Injuries and loss of form for just about every defender in the squad has led to failure. So what’s next?

A meeting between Klopp, sporting director Michael Zorc and CEO Hans-Joachim Watzke on Sunday resolved that no drastic changes would be made. The coach has the backing of the board, while players and supporters are still firmly behind him. On Monday evening, the club announced the signing of Salzburg’s playmaker Kevin Kampl. The 24-year-old should add creativity and poise in the middle of the field. Recent history is also on their side: they tend to have a good second half of the season under Klopp.

But there’s a second, deeper worry here, one that will render the next six weeks off perhaps even more restless for everyone at the club than a look at the table. Coaches who demand Klopp’s level of work and tactical discipline from their players don’t tend to last very long at any particular club. Think Guardiola, José Mourinho, Marcelo Bielsa, even Ralf Rangnick: wear and tear - physically, mentally and in terms of relationships - always become a problem before too long.

Klopp is in his seventh season at Borussia. In modern terms, that’s an eternity. But the young players who have followed his instructions so slavishly – so much so that one or two commentators compared BVB to a cult with Klopp as the spiritual leader – are now a little older, perhaps a little wiser but maybe a little slower as well. Almost as shocking as Dortmund’s ineptitude on Saturday was the tired emptiness Klopp radiated after the final whistle. 2014-15 won’t mark the end of BVB’s membership in the top-flight. But it could well be the beginning of the end of the Klopp era, with all the vagaries that go with it.

Bundesliga results

Mainz 1-2 Bayern, Augsburg 2-1 Gladbach, Bayer Leverkusen 1-1 Frankfurt, Schalke 0-0 Hamburg, Wolfsburg 2-1 Köln, Stuttgart 0-0 Paderborn, Werder Bremen 2-1 Dortmund, Hertha 0-5 Hoffenheim, Freiburg 2-2 Hannover