It can never be all flowers and roses in football. Things go wrong, players disappoint, and the people you think you can bank on to pull through for you can easily go missing. It's the nature of a high-pressure, unpredictable sport.
It's early days, but we've perused 15 top European clubs' performances and picked out their biggest disappointment, in the form of a player. It's the complete opposite of last week, where we selected revelations over who has shocked and wowed us.
There's still plenty of time for all of these players to turn things around, so hold the nails and put away the coffins, but at the very least, expect these 15 players to improve in the months to come.
AC Milan: Leonardo Bonucci
"I'm not satisfied because I've made several mistakes and I have not been accurate enough. I want to respond on the pitch to everything that has been said."
Leonardo Bonucci's assessment of his own performances so far in an AC Milan shirt, via Sempre Milan, have been brutally honest. He was one of the highest-profile transfers in the summer and arrived at the San Siro with great expectation but is yet to live up to it.
Milan bought a lot of players this summer and it was always going to take time for them to settle and jell, but one thing that was perhaps taken as guaranteed was that Bonucci would be an immediate force in defence. That hasn't quite happened yet.
Arsenal: Shkodran Mustafi
It's been an up-and-down start to the season for Arsenal who, as ever, have flitted between terrible and pretty good on a weekly basis. Many of their players have fluctuated in form as a result, but only a few of those can be termed disappointing.
Granit Xhaka's slow start belies his strong end to last season, while Hector Bellerin's been a bit off—although he started the season on the wrong flank to accommodate the now-departed Alex Oxlade-Chamberlain.
But one player who is still doing the same, reckless things is Shkodran Mustafi, and it's really starting to irritate fans. He makes so many risky tackles high up and walks the disciplinary line so closely every game. Sometimes he nails the challenges but quite often he doesn't, and opponents are becoming aware of it.
He did it last season and the hope was he would cut it out over the summer but that hasn't happened. He still plays too similarly to Nicolas Otamendi—a player who, perhaps tellingly, was his team-mate at Valencia before both moved to the Premier League.
Atletico Madrid: Kevin Gameiro
According to John Cross of the Daily Mirror, Kevin Gameiro is being sounded out by goal-shy Everton ahead of a potential January transfer. That's great news for Toffees fans, but not good news for Gameiro.
He's hardly featured so far this season for Atletico Madrid, once again failing to imprint on the team and impress Diego Simeone. He cost a lot, but that doesn't mean he's an automatic selection.
With Angel Correa taking clear steps forward this term with regard to consistency and ability to play well when starting, and Luciano Vietto scooping up minutes too, things do not look good for Gameiro.
Barcelona: Luis Suarez
What's going on with Luis Suarez at the moment?
His iffy run towards the end of last season has extended into this one; he's missing a lot of chances, and while it's not costing Barcelona right now, it could well do so soon.
Midweek brought a case in point: A narrow win over Sporting CP could have been much more comfortable had he buried one great chance, and he might have scored had he not scuffed a free-kick into Sebastian Coates, eventually resulting in an own goal, rather than one of his own.
There's no doubt Suarez will turn this around—he's one of the world's few elite strikers—but when? Barcelona are eagerly awaiting the point of change.
Bayern Munich: Sven Ulreich
Replacing Manuel Neuer is not an easy gig, but the now-departed Carlo Ancelotti and Bayern Munich would have been right to expect a lot more from Sven Ulreich so far in his stead.
He's been far from assured between the sticks, with the unfortunate phrase "floppy wrists" becoming attributed to him. He's beaten at his near post far too often too.
Bayern haven't hit the levels expected this season and many players have disappointed, but Ulreich is probably the biggest issue of them all.
Borussia Dortmund: Lukasz Piszczek
Where to turn to with BVB? They've been close to perfect in the Bundesliga, performing well in all three phases, conceding just once and nailing teams by huge margins.
In the Champions League, though, things have been a little different; they've lost both of their games there—albeit against strong opposition—and it has perhaps highlighted a weakness at right-back.
Lukasz Piszczek is most certainly slowing down (he's 32 now), and it was noticeable that Tottenham Hotspur picked on his flank during their meeting at Wembley Stadium early in September. All three goals came from his side.
Chelsea: Gary Cahill
Like so many teams on this list, Chelsea have generally started the season well. They're looking good in the Premier League and have just secured the first away victory at Atletico Madrid's new Wanda Metropolitano, so it's all smiles at the moment.
But one of the major reasons the Blues aren't shoulder-to-shoulder with the Manchester clubs at the top of the domestic table is that ridiculous opening home loss to Burnley, in which several parts of the team imploded.
In particular, Gary Cahill's early red card set them on the wrong course, so he features as the biggest disappointment so far. That's not how a newly appointed captain should start the season for the champions.
If we're being incredibly picky, he didn't impress on his league return against Arsenal either, with errant passing stunting the Blues' buildup play considerably.
Juventus: Gonzalo Higuain
A lack of form is the last thing you need from your €90 million striker, but that's exactly what Juventus are facing with Gonzalo Higuain.
He's been dropped by both Massimiliano Allegri and Jorge Sampaoli (for Argentina) in the last month and his confidence has taken an understandable hit as a result. His stat lines don't look bad at all, but for the most part he's been far too quiet—particularly in comparison to star compatriot Paulo Dybala.
He was benched for Juve's game against Olympiakos in midweek and was forced to answer his critics with a goal after coming on. Could that be the catalyst for an improvement in form?
Liverpool: Georginio Wijnaldum
Many will immediately think "defence" for Liverpool here, but the back line has been just as lacking as expected; just as lacking as last season. Given there were no major recruits in that area, nothing better could be expected.
The attack has looked good (if lacking that final touch still, at times) and with Sadio Mane returning from suspension, it's about to get a whole lot better again.
That just leaves the midfield. All three of Jordan Henderson, Emre Can and Georginio Wijnaldum have peaked and troughed, but it's the latter's fluctuation that has concerned the most. He's not even performing well in the big games, which was his calling card in 2016-17.
Manchester City: Benajmin Mendy (injury)
That Benjamin Mendy's season is probably over, having played just four Premier League games since arriving for a world-record fee for a full-back, is so gutting.
Regardless of where your allegiances lie, it's sad that such an exciting, effervescent character and player will be sidelined by a cruel injury for months.
On the pitch he's been great; Mendy has not been selected here for performance-related issues. But where else do you look in an unbeaten City side that has scored 21 and conceded just two in the league? There's no fault to apply, anywhere; goalkeeping and defending have improved hugely, and they're tearing teams apart up top.
Just as City welcome Ilkay Gundogan back from a long-term knee injury, they lose another to a similar fate. Football is savage.
Manchester United: Luke Shaw
On the one hand, it feels harsh to label a player a disappointment despite rarely even making the bench for Manchester United this season; on the other, that's exactly the problem when it comes to Luke Shaw.
The fans are desperate for him to find form and fitness and come good—they've been desperate for that to happen for over a year—but despite Jose Mourinho's eye-popping rotation at left-back, the Englishman's grabbed just one half of football against Burton Albion, with the score already at 3-0.
Each new season brings a fresh round of hope for Shaw's prospects at United, but so far this term things have turned out to be more of the disappointing same.
AS Monaco: Fabinho
Those predicting an AS Monaco collapse in 2017-18 have been left disappointed, but it's still obvious they're a weaker group than before. Despite Radamel Falcao's best efforts to cover that up, it's clear.
Surprisingly, one of the main sources of disappointments has been Fabinho—one of the faces who isn't at all new in this team. You can forgive any new recruit for taking a little time to bed in, but the Brazilian—the mastermind of last season's midfield—should be firing from the start.
Is that missed transfer away playing on his mind so heavily?
Paris Saint-Germain: Layvin Kurzawa
How do you pick a disappointment in what seems to be an all-conquering side? PSG are yet to lose a game, and the 0-0 draw with Montpellier last weekend won't trouble them for long; a big win over Bayern Munich helped them forget.
So, on to the perceived weakest link in this side, and it's Layvin Kurzawa at left-back. He still isn't convincing—even in a side that is battering teams and racking up goals—and that's magnified by the fact Dani Alves is so much better on the opposite flank.
Unai Emery knows the left is an issue post-Maxwell. He recruited Yuri Berchiche in the summer from Real Sociedad to add competition and he's looked OK, but he too is a limited player. Left-back could be an issue for PSG all season.
Real Madrid: Cristiano Ronaldo
There's no doubt about it: Cristiano Ronaldo's five-game suspension, ludicrously earned due to pushing a referee during the Spanish Super Cup, placed Real Madrid in an early hole this season.
With Alvaro Morata sold during the summer, it became clear the Portuguese was to be the only other senior striking option alongside Karim Benzema this season; when the Frenchman was injured, the club were forced to turn to the likes of Borja Mayoral.
You can label that bad planning—it is—but it's also an indictment on Ronaldo's mad moment. Those five games he was suspended for felt like 10; his presence is everything to the team, and he wasn't there for them.
Tottenham Hotspur: Kieran Trippier
Dele Alli was a consideration here. Just as in 2016-17, he has struggled to sparkle early on, and fans are left hoping he catches fire later.
But Kieran Trippier's failure to seize what was a golden chance to become Tottenham's starting right-back has disappointed many.
His early struggles surely played a part in the club's decision to sign Serge Aurier as a competitor/replacement, and what's been infuriating is that Trippier has been timid and scared on the ball. A refusal to drive forward has hurt the team's attacking shape, particularly at home.
All statistics via WhoScored.com