It's possible that no manager in European football has had a greater transformational effect on a club this century than Diego Simeone has had at Atletico Madrid.
Of course, it's impossible to actually prove/disprove that, but when you consider his eight trophy successes is almost a quarter of all the major silverware the club have ever won, most counterarguments would dissipate.
Yet 2021-22 has been far from smooth, and they could head into Sunday's trip to Villarreal 17 points behind pacesetters Real Madrid, assuming Los Blancos beat Valencia 24 hours earlier.
Part of Atletico's problem is they seem to have lost the defensive solidity that's been a cornerstone of Simeone's tactical plan in his decade at the club.
Sunday's match will be the first since the 10-year anniversary of his bow as Atletico coach on January 7, 2012, providing the opportunity to look at how much of a challenge this season is proving to be.
11 away games, no clean sheet
Nothing is more indicative of Atletico's current malaise than their struggles to shut teams out – they're not getting battered, but we're so used to seeing them boast the shrewdest defence in LaLiga.
That's simply not the case this season.
Their 22 goals conceded is bettered by seven teams and isn't far off being twice as many as Sevilla (13), LaLiga's strongest defence this term.
Atletico's issues have been particularly prominent on the road. They've not secured an away clean sheet in LaLiga in any of their previous 11 such games, which is their worst run since December 2010 (17 matches).
No team has more away clean sheets across the top five leagues than Atletico (85) since Simeone's first match, but Manchester City (82) are closing in, fast.
Missing home comforts
The away struggles alluded to before also translates to defeats, with Atletico losing each of the three most recent matches on their travels.
It's worth remembering that two of those came to Madrid and Sevilla, first and second in the table, but typically Simeone's Atletico are solid enough that such sequences don't occur, regardless of the opposition.
In fact, prior to this run, Atletico had not conceded two or more goals in three successive away league games since January/February 2014.
If they lose to Villarreal, it will be their first streak of four consecutive defeats on the road since December 2011, the month Simeone was appointed.
Yellow Submarine on the rise
It wasn't so long ago that Unai Emery appeared to be in danger of being sacked, then he held talks with Newcastle United but ultimately rejected them.
Some might even suggest that his show of loyalty then bought him a little more time at the Ceramica.
As it turns out, Villarreal staying their hand seems to have worked out well. While they may only be as high as eighth, fourth-placed Atletico are just four points ahead of them.
Their recent run has been crucial to that as well, having won each of their past four league games, the most successive LaLiga victories they've managed under Emery.
The end is Unai?
Atletico can perhaps take confidence from the fact Emery has a dreadful record against Simeone.
He has never beaten the Argentinian in 15 matches across all competitions, the most games Emery has managed against another coach without a win in his entire career.
On the flip side, every record or streak is there to be broken – this particular one surely cannot go on forever, and this is one of the more beatable Atletico teams Emery has faced.
He will hope the end of that particular run is nigh.