Every team and every person has them.
Superman can't deal with kryptonite, vampires shudder at the thought of daylight and Barcelona could do with a central defender.
When you spend over £100 million in a transfer window, it becomes slightly harder to find them, but scratch beneath the surface and Real Madrid do have some too.
Over the following slides, B/R list five weaknesses which could undo the Bernabeu side this season—although some may be stretching it.
He's managed two goals in his three league appearances for Real Madrid this season, yet the common feeling in the Spanish capital is that Karim Benzema does not possess the killer instinct to be a world-class forward.
Jeered by sections of the Bernabeu crowd in Madrid's last outing—a 3-1 win over Athletic Bilbao—the Frenchman has little opposition for his spot in the team.
Alvaro Morata, who scored five goals in the two recent Spain U-21 fixtures, is one option. However, he is unproven at the very top level.
There is Jese Rodriguez, too—another youngster with bags of talent. Like Morata, he could have a big Los Blancos future.
However, while Benzema is under pressure and the other two remain inexperienced, other teams will do well to prey on the situation, try to keep Cristiano Ronaldo and Gareth Bale quiet and sneak a low-scoring draw or win.
The media scrutiny on the goalkeeper situation in the Madrid press means there is more pressure put on the man who does get the No. 1 shirt.
At the moment, it is Diego Lopez, but he knows that any mistakes will present the perfect opportunity for Iker Casillas to be reinstated.
If Casillas does get the nod to return to the starting lineup, he'll do so with the knowledge that he is no longer undroppable—mistakes can be punished.
Opposing teams can try to take advantage of this by putting the Madrid 'keeper, whoever that may be, under as much pressure as possible.
Foul him, test him from distance, fire in crosses and generally try to make his life difficult.
On the face of it, Real Madrid have adequate cover on both the right and left side of their defence—however, things aren't quite that straightforward.
Dani Carvajal returned from Bayer Leverkusen this summer, but the youngster still seemingly finds himself behind Alvaro Arbeloa in the pecking order.
Arbeloa is a better right-back than many give him credit for, but he's also a right-back some of Spain's left-wingers will feel they can target in a strong Madrid side.
The left side brings Marcelo and Fabio Coentrao. Both good players, both injury prone.
Brazilian Marcelo spent large parts of last season injured, and is likely to miss this weekend's trip to Villarreal, too.
Also set to miss that trip is Coentrao, who has suffered from knee injuries in the past and looked set to leave the Bernabeu this summer.
It's all well and good having two good left-backs, but if neither can stay fit...
Three games, three wins and nine points sounds pretty good for Carlo Ancelotti and Real Madrid.
And while not being at your best and still winning is said to be the sign of a good team, there are signs that Madrid are still looking to find their feet under the guidance of their new Italian manager.
Athletic Bilbao were comfortably dispatched 3-1 most recently, though.
This is a team still jelling, as Ancelotti tries to change the style slightly. Isco has begun to show his potential, but fellow new signings Dani Carvajal, Asier Illarramendi and Gareth Bale are yet to properly feature—although the former did play 90 minutes in the opening week.
Once they do click, things could get out of hand pretty quickly, so teams playing Madrid in the coming weeks may want to seize that opportunity.
While Real Madrid won 1-0 at Granada, ending their Andalusia hoodoo, there were signs that they will still struggle against a certain type of team away from home.
Last season, they lost at Granada, Malaga, Sevilla, Real Betis and Getafe—that's over a quarter of their away matches.
They were also held to draws in another five fixtures on the road.
In their only away game this season, at Los Carmenes, they were fortunate to escape with a 1-0 win; Granada were denied a clear penalty and Piti's twisting and turning should have brought a stoppage time tap-in for Riki.
This weekend's visit to fellow table-toppers Villarreal could prove interesting.